Power cell and power chip architecture

ABSTRACT

A power cell comprises a membrane with a first side and a second side. The membrane has a geometric structure encompassing a volume. The power cell also has a cover that is coupled to the membrane to separate the first flow path from the second flow path at the membrane. In the power cell, first and second catalyst is in gaseous communication with respective first flow path and second flow path and in ionic communication with respective first and second sides of the membrane. Furthermore, a first electrode is electrically coupled to the first catalyst on the first side of the membrane, and a second electrode is electrically coupled to the second catalyst on the second side of the membrane. In another embodiment, the power cell further includes a substrate on which the membrane is coupled.

RELATED APPLICATIONS

This application is a Continuation-in-part of U.S. application Ser. No.11/521,593 filed Sep. 14, 2006, which is a Continuation of U.S.application Ser. No. 11/322,760, filed Dec. 29, 2005, now abandoned,which claims priority to and is a continuation application of U.S.application Ser. No. 10/953,038 filed on Sep. 29, 2004, now U.S. Pat.No. 6,991,866, and of U.S. application Ser. No. 10/985,736 filed on Nov.9, 2004, now U.S. Pat. No. 7,029,779, which are a divisional applicationand a continuation application, respectively, of U.S. application Ser.No. 09/949,301 filed Sep. 7, 2001, now U.S. Pat. No. 6,815,110, which isa continuation of U.S. application Ser. No. 09/449,377, filed Nov. 24,1999, now U.S. Pat. No. 6,312,846. This application also claims priorityto U.S. Application No. 60/778,584, filed Mar. 2, 2006 and U.S.Application No. 60/778,563, filed Mar. 2, 2006. The entire teachings ofthe above applications and patents are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Electro-chemical fuel cells are not new. Invented in 1839 by AlexanderGrove, electro-chemical fuel cells have recently been the subject ofextensive development. As environmental concerns mount and energylegislation toughens, development of “green” energy sources becomes morejustified as a course of action, if not required.

Within the last decade, development has addressed various types of fuelcells designed to address various applications and corresponding powerlevels, ranging from large stationary power plants (kilowatts tomegawatts), to transportation (bus, automobile, scooter), and to smallerelectronic devices (laptops, cell phones, PDAs).

In U.S. Pat. Nos. 6,312,846 and 6,815,110, Marsh describes an approachto Proton Exchange Membrane (PEM) fuel cells fabricated on asemiconductor substrate. Using conventional semiconductor fabricationmethods, such fuel cells can be made extremely small, in very greatquantity, and at very low cost on a single substrate.

SUMMARY OF THE INVENTION

In accordance with an example embodiment of the present invention, amethod and apparatus is provided which uses a combination ofself-assembled monolayers (SAMs), micro electrical mechanical systems(MEMS), “chemistry-on-a-chip” and semiconductor fabrication techniquesto create a scalable array of fuel cells directly on a substrate,preferably a semiconductor wafer. These wafers may be “stacked” (i.e.,electrically connected in series or parallel, as well as individuallyprogrammed to achieve various power (V*I) characteristics andapplication driven configurations.

One embodiment of the present invention is a power cell, e.g., fuelcell. The power cell comprises a membrane with a first and a secondside. The membrane has a three-dimensional geometric structureencompassing a volume. The power cell may also have a cover coupled tothe membrane to separate the first flow path from a second flow path atthe membrane. In the fuel cell, first and second catalyst may be ingaseous communication with respective first flow path and second flowpath and in ionic communication with respective first and second sidesof the membrane. Furthermore, a first electrode is electrically coupledto the first catalyst on the first side of the membrane, and a secondelectrode is electrically coupled to the second catalyst on the secondside of the membrane. In one embodiment, the power cell may furtherincludes a substrate to which the membrane is coupled.

One embodiment of the invention is a method of generating energy using apower cell. The method comprises flowing fuel or oxidant through avolume encompassed by a proton exchange membrane of the power cell.

One embodiment of the invention is a power chip that includes an arrayof power cells. The array of power cells includes a plurality ofmembranes, with first sides and second sides, having three-dimensionalgeometric structures encompassing respective volumes. At least one coveris coupled to the membranes to separate the first flow paths from atleast one second flow path at the membranes. The array of power cellsmay also include first and second catalyst in gaseous communication withthe first flow paths and the at least one second flow path,respectively, and in ionic communication with respective first andsecond sides of the membranes. In the array of power cells, at least oneplenum may be in gaseous communication with the first flow paths or theat least one second flow path to distribute the fuel or oxidant. Toprovide an interface to energy generated by the power cells, at leastone pair of terminals is electrically coupled to the first and secondcatalyst of at least a subset of the array of the power cells.

One embodiment of the invention is a method of generating energy using apower chip. The method comprises flowing fuel or oxidant through volumesencompassed by proton exchange membranes of an array of power cells.

One embodiment of the present invention is a power disk that includes anarray of power cells. The array of power cells of the power disk mayinclude a plurality of membrane, with first sides and second sides,having three-dimensional geometric structures encompassing respectivevolumes. At least one cover coupled to the membranes to separate thefirst flow paths from at least one second flow path at the membranes.The array of power cells can further include first and second catalystin gaseous communication with the first flow paths and the at least onesecond flow path, respectively, and in ionic communication withrespective first and second sides of the membranes. The power diskfurther includes at least one plenum in gaseous communication with thefirst flow paths or the at least one second flow path to distribute thefuel or oxidant. To provide an interface to energy generated by thepower cells, at least one pair of terminals is electrically coupled tothe first and second catalyst of at least a subset of the array of powercells. Furthermore, the power disk can include at least one power buselectrically coupled to the at least one pair of terminals.

Alternatively, in another embodiment, a power disk can include asubstrate and at least one power chip, which is coupled to thesubstrate. The power chip can include an array of three-dimensionalpower cells encompassing volumes, a plurality of chip flow paths ingaseous communication with the array of power cells to distribute fueland oxidant, and chip terminals electrically coupled to the array ofpower cells. At least one of the chip flow paths can be aligned with theat least one disk manifold. The power disk can further include at leastone power disk bus electrically coupled to the chip terminals.

Yet in another embodiment of a power disk, the power disk can include asubstrate and an array of power cells that is coupled to a substrate.The array of power cells can include a plurality of membranes, withfirst sides and second sides, having three-dimensional geometricstructures encompassing respective volumes. At least one cover can becoupled to the membranes to separate the first flow paths from at leastone second flow path at the membranes. First and second catalyst can bein gaseous communication with the first flow paths, and the at least onesecond flow path, respectively. The first and second catalyst canfurther be in ionic communication with respective first and second sidesof the membranes. Furthermore, the power disk can include a firstelectrode electrically coupled to the first catalyst on the first sideof the membrane and a second electrode electrically coupled to thesecond catalyst on the second side of the membrane. Furthermore, thepower disk can include a pair of power disk buses electrically coupledto the respective first electrode and the respective second electrode.

One embodiment of the invention is a method of generating energy using apower disk. The method includes flowing fuel or oxidant through asubstrate into volumes encompassed by an array of power cells.

One embodiment of the invention is a power stack. The power stackincludes a power stack structure associated with at least one stackmanifold, and a plurality of power disks, with respective power cells,coupled to the power stack structure. Each power disk can include atleast one substrate associated with at least one disk manifold ingaseous communication with the at least one stack manifold to distributefuel or oxidant to power chips coupled to the power disks. Each powerdisk can further include disk terminals electrically coupled to thepower chips. The power stack can further include power stack terminalsthat are associated with the power stack structure and configured to beelectrically coupled to the disk terminals.

Another embodiment of the invention is a method of generating energyusing a power stack. The method includes flowing fuel or oxidant throughat least one stack manifold to at least one disk manifold associatedwith power disks supporting power cells, and flowing the fuel or oxidantthrough the at least one disk manifold to the power cells.

One example embodiment of the invention is formed by fabricating aplurality of individual fuel cells on a planar semiconductor wafer intowhich flow channels are formed by etching or other well-knownsemiconductor processes. Oxygen is admitted into one side of a channeland hydrogen into the other side; with the two gases being separated bya membrane. Electrodes are formed on opposite sides of the membrane anda catalyst is provided in ionic communication with the electrode andmembrane on both sides. Lastly, a gas impermeable cover or lid isattached to the cell.

The substrate may be divided into individual fuel cell devices, eachsized to meet a particular power generation application. Alternatively,the full substrates may be assembled into a stack to generate largeramounts of power.

Because of the inherent three-dimensional nature of the fuel cells,embodiments of the present invention enable construction of fuel cellassemblies (power chips) with much higher reactive surface area per unitof substrate area than would otherwise be possible. This, in turn,creates a large advantage in power density and manufacturing cost.

In addition, a number of fuel cells can be electronically interconnectedand coupled to gas sources on at least a portion of the same substrateor same wafer to form a “power chip”. Traditional electrical circuitrycan be integrated on the wafer along with the chips to provide processmonitoring and control functions for the individual cells. Substrates orwafers containing multiple chips (power discs) or multiple cells canthen be stacked upon one another forming a power stack.

A further understanding of the nature and advantages of the inventionherein may be realized with respect to the detailed description whichfollows and the drawings described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a schematic plan view of a semiconductor fuel cell array inaccordance with the invention.

FIG. 2 is a simplified schematic cross-sectional view taken along thelines II-II of a fuel cell 12 of the invention.

FIGS. 3(a)-(h) is a schematic sectional process view of the major stepsin fabricating a PEM barrier structure 30 of the invention.

FIG. 4 is a cross-sectional schematic view illustrating an alternatecast PEM barrier invention.

FIG. 5 is a sectional view of a PEM structure embodiment.

FIG. 6 is a sectional view of an alternate of the PEM structure.

FIG. 7 is a sectional view of another alternate PEM structure.

FIG. 8 is a block diagram of circuitry which may be integrated onto afuel cell chip.

FIG. 9 is a schematic of the wiring for an integrated control system forthe operation of individual cells or groups of cells.

FIG. 10 is a schematic side view of a manifold system for a fuel cell.

FIG. 11 is a schematic plan view of a plurality of cells arrangedside-by-side on a wafer to form a power chip and stocked on top of eachother to form a power disc.

FIG. 12 is a fragmented side-view of FIG. 11.

FIG. 13 is a schematic plan view of a semiconductor fuel cell array inaccordance with an embodiment of the present invention.

FIG. 14 is a schematic view of a fuel cell in accordance with thepresent invention.

FIG. 15 is a simplified schematic cross-sectional view of the fuel cellof FIG. 14 of the present invention.

FIGS. 16A-16D are schematic cross-sectional views of the fuel cell inaccordance with embodiments of the present invention.

FIG. 17 is a schematic plan view of a PEM surface with “fins” toincrease the active areas in accordance with an embodiment of thepresent invention.

FIGS. 18A-18C are illustrations of comparing footprint areas between atypical two-dimensional fuel cell and fuel cell designs in accordancewith embodiments of the present invention.

FIGS. 19A and 19B are schematic plan views of the cover configuration ofthe fuel cell in accordance with an embodiment of the present invention.

FIGS. 20A and 20B are schematic plan view of a power stack in accordancewith an embodiment of the present invention, and a cross-sectionalschematic view illustrating the hierarchical construction of anexemplary power stack formed of multiple power disks, each of whichcontaining many power chips.

FIG. 21 is an illustration of incremental volumatic increase in powerdensity by stacking the fuel cells in accordance with an embodiment ofthe present invention.

FIG. 22 is an illustration of incremental gravimetric increase in powerdensity by stacking the fuel cells in accordance with an embodiment ofthe present invention.

FIG. 23 is a circuit diagram illustrating prior art with respect togeneration of regulated power from a battery, fuel cell, or other suchdevice.

FIG. 24 is a plot illustrating a typical voltage-current (V-I) curve fora micro fuel cell, as well as variation with ambient conditions.

FIG. 25 is an example showing inter-connection topology of aseries-parallel, switched arrangement of fuel cells.

FIG. 26 is a plot showing variation of voltage with output current andwith the number of columns switched into the circuit as a load impedanceis decreased.

FIG. 27 is an example switching topology for a series column of avariable number of fuel cells.

FIG. 28 is a plot illustrating a transient response typical of a fuelcell after it is switched into an operational set on state.

FIG. 29 is a schematic diagram illustrating a typical transfer functionof a fuel cell.

FIG. 30 is a block diagram of an example closed loop control system usedto accomplish voltage regulation and optimal fuel usage for an array offuel or power cells.

FIG. 31 is a flow chart of an example control process incorporated intoa control system used to operate power cells, such as fuel cells.

FIG. 32 is a flow chart for the control process of FIG. 9, incorporatingadaptation for temperature, humidity, pressure, and device failure.

FIG. 33 is a plot that indicates how the V-I curve of an aggregate arrayof fuel cells varies with the number of series-connected fuel celldevices in a column.

FIG. 34 is a plot that indicates how the V-I curve of an aggregate arrayof fuel cells varies with the number of parallel-connected fuel celldevices in a row.

FIGS. 35A and 35B are plots that indicate total power generated,internal power dissipation, power delivered to the load, and powerefficiency for a typical V-I curve.

FIGS. 36A and 36B are a circuit schematic diagram and correspondingfunctional plot of current, respectively that illustrate energy lostthrough repeated on-off switching of a power cell to maintain anintermediate average value.

FIG. 37 is a switching topology of a fuel cell array configured tosupply multiple, independently regulated voltages.

FIG. 38 is a block diagram of an array of power cells used to generatepower in a power amplifier configuration.

FIG. 39 is a block diagram illustrating an output waveform generated byan array of power cells controlled to adjust an output power tocompensate for effects of a load.

FIG. 40 is a block diagram of an example array of power cells havingzones sequentially or otherwise selected to deliver power to a load.

FIG. 41 is a block diagram of an array of power cells operated in amanner to warm up the power cells during an example start-up sequence.

FIG. 42 is a functional diagram of a controller having kernel (basic)functions and higher functions configured to employ the kernelfunctions.

FIG. 43 is a schematic diagram of a power cell being connected to otherpower cells that generate a pulse or other waveform to cleancontaminants from the cell receiving the pulse or other waveform.

FIG. 44 is a schematic plan view of a power cell for conductingelectro-chemical reaction.

DETAILED DESCRIPTION OF THE INVENTION

A description of example embodiments of the invention follows.

Referring now to FIG. 1, there is shown in plan view a conventionalsemiconductor wafer 10 upon which a plurality of semiconductor fuelcells 12 have been fabricated. A plurality of cells may be electricallyinterconnected on a wafer and provided with gases to form a power chip15. For simplicity, fuel cells 12 and chips 15 are not shown to scale inas much as it is contemplated that at least 80 million cells may beformed on a 4″ wafer. One such cell is shown in fragmented cross-sectionin FIG. 2. In its simplest form, each cell 12 consists of a substrate14, contacts 16A and B, and a conductive polymer base 18 formed on bothsides of a first layer 20(a) of non-conductive layered polymer supportstructure 20 and in intimate contact with the metal electrical contacts.

A conductive polymer 22 with embedded catalyst particles 28 on bothsides of the central structure 20 forms a PEM barrier separating thehydrogen gas on the left side from the oxygen gas on the right side.Etched channels 50B and 50A respectively for admittance of the O₂ and H₂gas and a heatsink lid 40 over the cell 12 is also shown in FIG. 2.

FIGS. 3 a-3 h are a series of schematic sectional views showing therelevant fabrication details of the PEM barrier 30 in several steps.FIG. 3 a shows the bottom of a fuel cell channel which has been etchedinto the semiconductor substrate 14. It also shows the metal contacts 16which are responsible for conveying the electrons out of the fuel cell12 to the rest of the circuitry. These metal contacts are deposited bywell-known photolithographic processes in the metalization phase of thesemiconductor fabrication process.

FIG. 3 b shows the conductive polymer base 18 as it has been applied tothe structure. Base 18 is in physical/electrical contact with the metalcontacts 16 and has been adapted to attract the conductive polymer 22 ofthe step shown in FIGS. 3 a-3 h.

FIG. 3 c shows the nonconductive polymer base 20(a) as it has beenapplied to the structure. It is positioned between the two conductivepolymer base sites 18 and is adapted to attract the nonconductivepolymer 20.

FIG. 3 d shows a polymer resist 21 as applied to the structure. Resist21 is responsible for repelling the polymers and preventing their growthin unwanted areas.

FIG. 3 e shows the first layer 20B of nonconductive polymer as it hasbeen grown on its base 20A. This is the center material of the PEMbarrier. It helps support the thinner outer sides 22 when they areconstructed.

FIG. 3 f shows the subsequent layers of nonconductive polymer 20 whichare laid down, in a layer by layer fashion to form a vertical barrier.This vertical orientation allows for area amplification.

FIG. 3 g shows the first layer 22 a of conductive polymer grown on itsbase 18. This is the outside wall material with catalyst of the PEMbarrier.

FIG. 3 h shows the subsequent layers of conductive polymer 22 laid down,in a layer by layer fashion on to the structure. FIG. 2 shows thecompleted structure after removal of the polymer resist layer 21 and theaddition of lid 40 and the pre-existing sidewalls 52 left out of FIGS. 3a-3 h for simplicity. This resist removal may not be necessary if layer21 was originally the passivation layer of the final step in thesemiconductor fabrication process.

Referring now to FIG. 2 again further details of the elements formingthe fuel cell 12 will be explained. The protein exchange membrane isshown generally at 30 forms a barrier between the fuel H₂ and theoxidant O₂.

The PEM barrier 30 is made up of three parts of two materials. There isthe first outside wall 22B, then the center 20, and finally the secondoutside wall 22C. It is constructed with a center piece 20 of the firstmaterial in contact with the two outside walls which are both made ofthe second material.

The material 20 forming the center piece is preferably an ionic polymercapable of passing the hydrogen ions (protons) through from the hydrogenside to the oxygen side. It is electrically nonconductive so that itdoes not, effectively, short out the power cell across the two contacts16A and 16B. It may be made of Nafion® or of a material of similarcharacteristics. An external load 5 as shown in dotted lines may becoupled across the contacts to extract power.

The second material 22, forming the two outside walls, is also a similarionic polymer capable of passing the hydrogen ions. In addition, it isdoped with nano catalyst particles 28 (shown by the dots), such as,platinum/alloy catalyst and is also electrically conductive.

By embedding the catalyst particles 28 into the polymer 22, maximumintimate contact is achieved with the PEM 30. This intimate contactprovides a readily available path which allows the ions to migratefreely towards the cathode electrode 16B. Catalysis is a surface effect.By suspending the catalytic particles 28 in the polymer 22, effectiveuse of the entire surface area is obtained. This will dramaticallyincrease the system efficiency.

By making the second material 22 electrically conductive, an electrodeis produced. The proximity of the electrode to the catalytic reactionaffects how well it collects electrons. This method allows the catalyticreaction to occur effectively within the electrode itself. This intimatecontact provides a readily available path which allows the electrons tomigrate freely towards the anode 16A. This will allow for the successfulcollection of most of the free electrons. Again, this will dramaticallyincrease the system efficiency.

In addition to the electrical and chemical/functional characteristics ofthe PEM 30 described above, there are some important physical ones thatare described below:

This self assembly process allows for the construction of a more optimumPEM barrier. By design it will be more efficient.

First, there is the matter of forming the separate hydrogen and oxygenpath ways. This requires that the PEM structure to be grown/formed sothat it dissects the etched channel 50 fully into two separate channels50A, 50B. This means that it may be patterned to grow in the center ofthe channel and firmly up against the walls of the ends of the powercell. It may also be grown to the height of the channel to allow it tocome into contact with an adhesive 42 on the bottom of lid 40.

Second, there is the matter of forming a gas tight seal. This requiresthat the PEM structure 30 be bonded thoroughly to the base structures 18and 20A, the substrate 14 and the end walls (not shown) of the powercell and to an adhesive 42 which coats the lid 40. By proper choice ofthe polymers, a chemical bond is formed between the materials theycontact in the channel. In addition to this chemical bond, there is thephysical sealing effect by applying the lid 40 down on top of the PEMbarrier. If the height of the PEM 30 is controlled correctly, thepressure of the applied lid forms a mechanical “O ring” type of selfseal. Growing the PEM 30 on the substrate 14 eliminates any fineregistration issues when combining it with the lid 40. There are no finedetails on the lid that require targeting.

Turning now to FIG. 4, there is shown in simplified perspective analternate embodiment of a PEM barrier involving a casting/injectingprocess and structure.

Using MEMS machining methods three channels 60A, 60B and 60C are etchedinto a semiconductor substrate 140. The outside two channels 60A and 60Care separated from the middle channel 60B by thin walls 70A, 70B. Thesewalls have a plurality of thin slits S₁ . . . S_(n) etched into them.The resultant tines T₁ . . . T_(n+1) have a catalyst 280 deposited onthem in the area of the slits. At the bottom of these thin walls, 70A,70B, on the side which makes up a wall of an outside channel 60A, 60C, ametal electrode 160A, 160B is deposited. A catalyst 280 is deposited onthe tines after the electrodes 160 are in place. This allows thecatalyst to be deposited so as to come into electrical contact and tocover to some degree, the respective electrodes 160 at their base. Inaddition, metal conductors 90 are deposited to connect to each electrode160, which then run up and out of the outside channels.

A lid 400 is provided with an adhesive layer 420 which is used to bondthe lid to the substrate 140. In this way, three separate channels areformed in the substrate; a hydrogen channel 60A, a reaction channel 60B,and an oxygen channel 60C. In addition, the lid 400 has variousstrategically placed electrolyte injection ports or holes 500. Theseholes 500 provide feed pathways that lead to an electrolyte membrane ofpolymer material (not shown) in the reaction channel 60B only.

The structure of FIG. 4 is assembled as follows:

First, the semiconductor fabrication process is formed includingsubstrate machining and deposition of all electrical circuits.

Next, the lid 400 is machined and prepared with adhesive 420. The lid400 is bonded to the substrate 140. Then, the electrolyte (not shown) isinjected into the structure.

The thin walls 70A, 70B of the reaction channel 60B serve to retain theelectrolyte during its casting. The slits S₁ . . . S_(N) allow thehydrogen and oxygen in the respective channels 60A, 60B access to thecatalyst 280 and PEM 300. Coating the tines T₁ . . . T_(1+n) with acatalyst 280 in the area of the slits provides a point of reaction whenthe H₂ gas enters the slits. When the electrolyte is poured/injectedinto the reaction channel 60B, it fills it up completely. The surfacetension of the liquid electrolyte keeps it from pushing through theslits and into the gas channels, which would otherwise fill up as well.Because there is some amount of pressure behind the application of theelectrolyte, there will be a ballooning effect of the electrolyte'ssurface as the pressure pushes it into the slits. This will cause theelectrolyte to be in contact with the catalyst 280 which coats the sidesof the slits S₁ . . . S_(N). Once this contact is formed and themembrane (electrolyte) is hydrated, it will expand even further,ensuring good contact with the catalyst. The H₂/O₂ gases are capable ofdiffusing into the (very thin, i.e. 5 microns) membrane, in the area ofthe catalyst. Because it can be so thin it will produce a more efficienti.e. less resistance (I²R) losses are low. This then puts the threecomponents of the reaction in contact with each other. The electrodes160A and 160B in electrical contact with the catalyst 280 is the fourthcomponent and provides a path for the free electrons [through anexternal load (not shown)] while the hydrogen ions pass through theelectrolyte membrane to complete the reaction on the other side.

Referring now to the cross-sectional views of FIGS. 5-7, variousalternate configurations of the PEM structure 30 of the invention willbe described in detail. In FIG. 5, the central PEM structure 20 isformed as a continuous nonconductive vertical element, and theelectrode/catalyst 16/28 is a non-continuous element to which lead wires90 are attached. FIG. 6 is a view of an alternate PEM structure in whichthe catalyst 28 is embedded in the non-conductive core 20 and theelectrodes 16 are formed laterally adjacent the catalyst. Lastly, inFIG. 7, the PEM structure is similar to FIG. 5 but the center core 201is discontinuous.

FIG. 8 is a schematic block diagram showing some of the possiblecircuits that may be integrated along with a microcontroller onto thesemiconductor wafer 10 to monitor and control multiple cellsperformance. Several sensor circuits 80, 82, 84 and 86 are provided toperform certain functions.

Temperature circuit 80 provides the input to allow the micro processor88 to define a thermal profile of the fuel cell 12. Voltage circuit 82monitors the voltage at various levels of the configuration hierarchy orgroup of cells. This provides information regarding changes in the load.With this information, the processor 88 can adjust the systemconfiguration to achieve/maintain the required performance. Currentcircuit 84 performs a function similar to the voltage monitoring circuit82 noted above.

Pressure circuit 86 monitors the pressure in the internal gas passages50A, 50B. Since the system's performance is affected by this pressure,the microprocessor 88 can make adjustments to keep the system running atoptimum performance based on these reading. An undefined circuit 81 ismade available to provide a few spare inputs for the micro 88 inanticipation of future functions.

In addition, configuration circuit 94 can be used to control at leastthe V*I switches to be described in connection with FIG. 9. The outputvoltage and current capability is defined by the configuration of theseswitches. Local circuitry 92 is provided as necessary to be dynamicallyprogrammed, such as the parameters of the monitoring circuits. Theseoutputs can be used to effect that change. Local subsystems 94 are usedby the micro 98 to control gas flow rate, defect isolation and productremoval. A local power circuit 96 is used to tap off some part of theelectricity generated by the fuel cell 12 to power the onboardelectronics. This power supply circuit 96 will have its own regulationand conditioning circuits. A two-wire communications I/F device 98 maybe integrated onto the chip to provide the electrical interface betweencommunicating devices and a power bus (not shown) that connects them.

The microcontroller 8 is the heart of the integrated electronicssubsystem. It is responsible for monitoring and controlling alldesignated system functions. In addition, it handles the communicationsprotocol of any external communications. It is capable of “in circuitprogramming” so that its executive control program can be updated asrequired. It is capable of data storage and processing and is alsocapable of self/system diagnostics and security features.

Referring now to FIG. 9, further details of the invention are shown. Inthis embodiment, the individual power cells 12 ₁, 12 ₂ . . . 12 ₄ areformed on a wafer and wired in parallel across power buses 99A and 99Busing transistor switches 97 which can be controlled from themicroprocessor 88 of FIG. 8. Switches 97B and 97A are negative andpositive bus switches respectively, whereas switch 97C is a seriesswitch and switches 97D and 97E are respective positive and negativeparallel switches respectively.

This allows the individual cells or groups of cells (power chip 15) tobe wired in various configurations, i.e., parallel or series. Variousvoltages are created by wiring the cells in series. The current capacitycan also be increased by wiring the cells in parallel. In general, thepower profile of the power chip can be dynamically controlled to achieveor maintain a “programmed” specification. Conversely, the chip can beconfigured at the time of fabrication to some static profile and thus,eliminate the need for the power switches. By turning the switches onand off and by changing the polarity of wiring one can produce both ACand DC power output.

To implement a power management subsystem, feedback from the powergeneration process is required. Circuitry can be formed directly on thechip to constantly measure the efficiencies of the processes. Thisfeedback can be used to modify the control of the system in a closedloop fashion. This permits a maximum level of system efficiency to bedynamically maintained. Some of these circuits are discussed next.

The quality of the power generation process will vary as the demands onthe system change over time. A knowledge of the realtime status ofseveral operational parameters can help make decisions which will enablethe system to self-adjust, in order to sustain optimum performance. Theboundaries of these parameters are defined by the program.

For example, it is possible to measure both the voltage and the currentof an individual power cell or group of power cells. The power outputcan be monitored and if a cell or group is not performing, it can beremoved if necessary. This can be accomplished by the power switches 97previously described.

An average power level can also be maintained while moving the active“loaded” area around on the chip. This should give a better overallperformance level due to no one area being on 100% of the time. Thisduty cycle approach is especially applicable to surge demands. Theconcept here is to split the power into pieces for better cellutilization characteristics.

It is expected that the thermal characteristics of the power chip willvary due to electrical loading and that this heat might have an adverseeffect on power generation at the power cell level. Adequate temperaturesensing and an appropriate response to power cell utilization willminimize the damaging effects of a thermal build up.

The lid 40 is the second piece of a two-piece “power chip” assembly. Itis preferably made of metal to provide a mechanically rigid backing forthe fragile semiconductor substrate 14. This allows for easy handlingand provides a stable foundation upon which to build “power stacks”,i.e., a plurality of power chips 15 that are literally stacked on top ofeach other. The purpose is to build a physical unit with more power.

FIG. 10 illustrates how the fuel 50A and oxidant/product channels 50A(and 50B not shown) may be etched into the surface of the substrate 14.These troughs are three sided and may be closed and sealed on the topside. The lid 40 and adhesive 42 provides this function of forming ahermetic seal when bonded to the substrate 14 and completes thechannels. A matrix of fuel supply and oxidant and product water removalchannels is thereby formed at the surface of the substrate.

The lid 40 provides a mechanically stable interface on which theinput/output ports can be made. These are the gas supply and waterremoval ports. The design may encompass the size transition from thelarge outside world to the micrometer sized features on the substrate.This is accomplished by running the micrometer sized channels to arelatively much larger hole H. This larger hold will allow for lessregistration requirements between the lid and substrate. The large holesin the lid line up with the large holes in the substrate which havemicrometer sized channels also machined into the substrate leading fromthe large hole to the power cells.

Each wafer may have its own manifolds. This would require externalconnections for the fuel supply, oxidant and product removal. Theexternal plumbing may require an automated docking system.

FIGS. 11 and 12 illustrates one of many ways in which several cells 12(in this example three cells side-by-side can be formed on a wafer 14 toform a power chip 15. Power disks can be stacked vertically upon eachother to form a vertical column with inlet ports, 50HI, 50OIrespectfully coupled to sources of hydrogen and oxygen respectively. Thevertical column of wafers with power chips formed therein comprises apower stack (93).

FIG. 12 illustrates how stacking of a number of power discs 15 maybeused to form power stacks (93) with appreciable power. The use of theword “stacking” is reasonable for it suggests the close proximity of thewafers, allowing for short electrical interconnects and minimalplumbing. In reality, the stacking actually refers to combining theelectrical power of the wafers to form a more powerful unit. They needonly to be electrically stacked to effect his combination. However, itis desirable to produce the most amount of power in the smallest spaceand with the highest efficiencies. When considering the shortestelectrical interconnect (power bussing) alternatives, one should alsoconsider the possibility of using two of the main manifolds aselectrical power busses. This can be done by electrically isolatingthese manifold/electrical power buss segments and using them to conveythe power from each wafer to the next. This reduces the big power wiringrequirements and permits this function to be done in an automatedfashion with the concomitant increased accuracy and reliability.

A desirable manifold design would allow for power disc stacking. In thisdesign the actual manifold 95 would be constructed in segments, eachsegment being an integral part of the lid 40. As the discs are stacked amanifold (tube) is formed. This type of design would greatly reduce theexternal plumbing requirements. Special end caps would complete themanifold at the ends of the power stack.

In summary of the disclosed embodiment thus far, one of the primaryobjects of this invention is to be able to mass produce a power chip 15comprised of a wafer 10 containing multiple power cells 12 on each chip15 utilizing quasi standard semiconductor processing methods. Thisprocess inherently supports very small features. These features (powercells), in turn, are expected to create very small amounts of power percell. Each cell will be designed to have the maximum power the materialcan support. To achieve any real substantially power, many millions willbe fabricated on a single power chip 15 and many power chips fabricatedon a “power disc” (semiconductor wafer 10). This is why reasonable poweroutput can be obtained from a single wafer. A 10 uM×10 uM power cellwould enable one million power cells per square centimeter. The finalpower cell topology will be determined by the physical properties of theconstituent materials and their characteristics.

The basic electro-chemical reaction of the solid polymer hydrogen fuelcell is most efficient at an operating temperature somewhere between 80to 100 C. This is within the operating range of a common semiconductorsubstrate like silicon. However, if the wafers are stacked additionalheatsinking may be required. Since a cover is needed anyway, making thelid 40 into a heatsink for added margin makes sense.

The fuel and oxidant/product channels are etched into the surface of thesemiconductor substrate. These troughs are three-sided and may be closedand sealed on the top side. The lid 40 provides this function. It iscoated with an adhesive to form a hermetic seal when bonded to thesemiconductor substrate and completes the channels. This forms a matrixof fuel supply and oxidant and product water removal channels at thesurface of the semiconductor substrate. The power cells two primarychannels are themselves separated by the PEM which is bonded to thissame adhesive. Thus, removing any fine grain is helpful in achievingalignment requirements.

Power Cell and Power Chip Architecture

It should be understood that the power cells described above may includea membrane having a three-dimensional geometric structure thatencompasses a volume and a cover coupled to the membrane to separate afirst flow path from a second flow path at the membrane. Herein, “apower cell” and “fuel cell” are synonymous and used interchangeably. Thepower cell may also include an anode catalyst layer, a cathode catalystlayer on the cover. Optionally, the power cell may include a substratehaving holes for flow of fuel or oxidant to the catalyst. Anotherembodiment of the present invention is a power chip. The power fuelcomprises an array of the power cells of the first embodiment with amanifold in gaseous communication with the first flow paths or at leastone of the second flow paths to distribute the fuel or oxidant. Thepower chip also includes terminals electrically coupled to the first andsecond catalyst to provide an interface to energy generated by the powercells. The electrical interconnect may extend between the power cellsand switches, fuses, or metal links for the purpose of configuring thearray or a subset of the array and interfacing with an external load.The configuration of the power chip may be programmable and may includecontrol electronics elements, such as switches. The power chip mayfurther include bond pads and package supporting stacks of the powerchips.

Another embodiment of the present invention is a power disk thatcomprises an array of the fuel cells described in the first embodimentwith the substrate electrically interconnecting electrodes with catalystand optionally to an external load. The electrical interconnect mayextend between the fuel cells and switches, fuses, or metal links in aconfigurable manner. The configuration of the power chip may beprogrammable. The power disk may further include bond pads and packagesupporting stacks of the power chips.

Yet in another embodiment of the present invention is the power stack.The power stack comprises an array of the power disks with a pluralityof the power disks, packaging including an electrical interconnection,packaging including a parallel gas flow interconnect, and a system ofmanifold(s) enclosing the array of fuel cells to distribute the fuel oroxidant.

Other embodiments may include combinations of the following which shallbe described in further details: a fuel cell with selected plan viewgeometric shape(s) (e.g., circle, square, serpentine), a castellation ofwall, a corrugation (fins on wall), a catalyst on cover, a coverstructure “low power” and “high power, a bidirectional operation means(electrolyzer and fuel cell), and a generalized micro-scale chemicalreactor on a chip.

FIG. 13 shows a plan view of a conventional semiconductor wafer 1305upon which a plurality of semiconductor fuel cells have been fabricated.Upon this wafer 1305 are constructed a plurality of power chips 1310using, with a few exceptions described below, standard andwell-established semiconductor and micro-electrical mechanical systemsfabrication methods. For simplicity, the power chips 1310 are not shownto scale.

After manufacture and wafer-level testing, the power chips may beseparated and packaged as individual power-generation devices, eachcontaining one copy of the integrated circuit that is being produced.Each one of these devices is called a “die”.

The dimensions of each individual die may be 1 cm² or smaller or largeras dictated according to the needs of the application of the power chip.

It should be understood that the substrate 1305 may be other forms ofsubstrate, such as metal, glass, silicon carbine and so forth.

FIG. 14 describes the elements of a power chip 1410. Each power chipincludes several subcomponents. Each power chip can be constructed on asubstrate 1405, such as a standard silicon wafer, upon which areconstructed a large plurality of fuel cells 1412 by means of variousMEMS fabrication steps. Metal layers 1416, 1415 a, and 1415 b areapplied to the silicon and etched to form a suitable electricalinterconnection network among the power cells 1412. Suitable insulationlayers 1420, following conventional semiconductor practices, interleavethe metal layers to provide electrical insulation and chemical,mechanical and environmental protection.

Bond pads 1425 are constructed at the edges of the power chip 1410,again following conventional practices, and provide a means ofelectrical connection between the power chip 1410 to external circuits(not shown). Bond leads (not shown) may connect to a circuit board usingcustomary chip-on-board methods, or to contacts (not shown) at the edgeof a molded package which facilitates stacking of multiple power chipsas described below.

In addition, the silicon area underneath and between the power cellstructures 1412 of the power chip 1410 may contain control electronicscircuit elements 1430. These circuit elements 1430 include, but are notlimited to, embedded control circuits, RAM or FLASH or ROM memory, logicin, for example, digital Application Specific Integrated Circuit (ASIC)form, A/D, sense and switching devices, which, taken together, maysupervise, control, optimize and report to external devices and/or otherfuel cells upon the operation of the power chip 1410.

FIG. 15 shows a perspective view of a vertical cross section of anembodiment of an individual fuel cell 1500. In accordance with oneembodiment of a fuel cell of the present invention, a Proton ExchangeMembrane (PEM) wall 1505 is configured to form a three-dimensionalgeometric structure, defining a volume 1507 of a first flow path 1510.That is, in the example of FIG. 15, the PEM wall 1505 encompasses avolume 1507 in shape of, for example, cylindrical shape and defines aportion of the first flow path. A cover 1520 is coupled to the top ofthe three dimensional geometrical structure formed by the PEM wall 1505structure creating a closed chamber and separating the first flow path1510 from a second flow path 1515 at the PEM wall 1505. While couplingthe cover 1520 to the PEM wall 1505 seals one end of the volume 1507,the opposite end of the volume 1507 closer to the entrance of the firstflow path 1510 is open, thereby, accessible to a flow of oxidant orfuel.

The cover 1520 may made of a gas impermeable material to preventshorting out between oxidant and fuel and can be made from a differentmaterial or the same material from that of the PEM wall 1505. The PEMwall 1505 is preferably an ionic polymer capable of passing the hydrogenions (protons) through from the hydrogen side to the oxygen side. ThePEM wall 1505 is electrically nonconductive so that it does not,effectively, electrically short out the fuel cell 1500 across an anode1530 and cathode 1535 on opposite sides of the PEM wall 1505. The PEMwall 1505 may be made of Nafion® or of a material of similarcharacteristics. A load (not shown) may be coupled across contacts (e.g.metal wires 1545 a, 1545 b) electrically connected to the anode 1530 andcathode 1535 to extract power during operation of the fuel cell 1500.Additionally, the PEM wall 1505 can be doped with catalyst particles,such as platinum/alloy catalyst that are electrically conductive.

In one embodiment, the power cell includes a substrate 1540, which cansupport the fuel cell 1500, as described above. However, the substrate1540 is an optional feature for the fuel cell 1500. In other words,because the PEM wall 1505 is a three-dimensional structure, the PEM wall1505 can be an autonomous structure that can stand upright by itself;therefore, the substrate 1540 is not a necessary component for the fuelcell 1500 of the present invention. When the substrate 1540 is employed,the PEM wall 1505 can be coupled to the substrate at a location throughwhich the fuel or oxidant can flow into the volume 1507. Furtherseparating the first flow path 1510 and the second flow path 1515, thecover 1520 is now coupled to PEM wall 1505 by a method commonly known byone skilled in the art.

In one embodiment, the cover 1520 can be attached using an appropriatecombination of heat, solvent, adhesive, and sonic welding and/ordownward pressure. For example, it can be patterned and etched. Allthese methods that are familiar in semiconductor manufacturing practicescan be applied. For example, PEM wall 1505 is bonded thoroughly to thesubstrate 1540 to form a gas tight seal by an adhesive. Alternatively,the cover 1520 and PEM wall 1505 can be attached by forming a chemicalbond between the materials, for example, using a polymer. In addition tothis chemical bond, there is the physical sealing effect by applying thecover 1520 down on the top 1509 of the PEM wall 1505. If the height ofthe PEM wall 1505 is controlled correctly, the pressure of the appliedcover can form a mechanical “O-ring” type of self seal. Growing the PEMwall 1505 on the substrate 1540 can eliminate any fine registrationissues when combining it with the cover.

In some embodiments, the cover 1520 being in contact with the top of thethree-dimensional structure can be made “active” (i.e., havingelectrodes covered with respective catalyst on each side in similarconfiguration as the cylinder walls), thereby increasing active surfacearea for production of electricity. Furthermore, it should be understoodthat a third material (not shown), non-gas permeable, can be constructedto the top of the PEM wall 1505, and the cover 1520 can be affixed tothe PEM wall 1505 via the third material. For example, a spacer (notshown) can be placed on top 1509 of the PEM wall 1505 so that the cover1520 is not in physical contact with any part of the PEM wall 1505 whilemaintaining gaseous communication with the first flow path 1510 forproduction of electricity.

In another embodiment, depending upon the specific sequence of processsteps employed in fabrication, the catalyst coating may extend to one orboth sides of the cover as well, further increasing the reactive surfacearea of the device. Alternatively, the first layer of the cover can beprovided with an adhesive layer which is used to bond the cover to thetop of the three-dimensional structure shown in FIG. 15.

Continuing to refer to the fuel cell 1500 shown in FIG. 15, the metal1545 a and metal 1545 b are two separate metal layers separated byinsulation layers 1506. Metal 1545 a is connected to the fuel cellcathode 1535, and metal 1545 b is connected to the fuel cell anode 1530.The anode 1530 and the cathode 1535 are separated by a layer of the PEMwall 1505.

In one embodiment, the catalyst 1530 and 1535 are embedded on the sidesof the PEM wall 1505. By embedding the catalyst, maximum intimatecontact is achieved with the PEM wall 1505. Catalysis is a surfaceeffect. This intimate contact provides a readily available path whichallows the ions to migrate freely towards the cathode 1535. Bysuspending the catalysis in the PEM wall 1505, effective use of theentire surface area is obtained. This can dramatically increase thesystem efficiency.

Gaseous fuel (e.g. hydrogen) 1585 (i) can be introduced into the volume1507 through hole(s) 1512 in the substrate 1540 facilitating the firstflow path 1510 at the fuel cell 1500 and (ii) is reduced by contact withthe anode catalyst 1530. Electrons resulting from this reaction travelthrough the conductive catalytic layer to the metal 1545 b and, in turn,to the load (not shown). Protons resulting from the reaction travelthrough the PEM wall 1505 to the cathode 1535. Oxidant 1550 (e.g.oxygen) available via the second flow path 1515 at the cathode 1535 atthe fuel cell 1500 from ambient air 1555 combines with the protonsflowing through the PEM wall 1505 and electrons arriving from the loadvia metal 1545 a to produce water vapor.

Alternatively, the anode 1530 and cathode 1535 can be assembled in theopposite configuration, where the anode 1530 is connected to one metal1545 a, and the cathode 1535 is connected to the other metal 1545 b. Insuch a configuration, gaseous fuel is introduced via the second flowpath 1515, and the oxidant is introduced via the first flow path 1510.

The PEM material can be initially deposited on the substrate or thewafer by means of spin coating, spraying, dipping, or other methodsconventionally used in semiconductor manufacturing. The PEM material canthen be photolithographically patterned and etched to form the wallcontours shown as the PEM wall 1505 in FIG. 15. The catalyst layers 1530and 1535 may be applied to the PEM as a coating, again usingconventional semiconductor fabrication methods with an appropriatecombination of sputtering, evaporating, spraying, transfer printing, andimmersion. The resulting catalyst layer may have a plurality of sublayers, constructed specifically to support the conflicting requirementsof large surface area to contact the ambient gas and to maintain (i)ionic conductivity to support proton transfer to the PEM and (ii)electrical conductivity to support electron transfer to the metal layerson the substrate. Due to the multiple layers of the catalyst, effectiveuse of the entire surface is obtained.

Although FIG. 15 shows a fuel cell of cylindrical form, other shapes arepossible, depending on performance characteristics desired for aparticular application. For example, the shapes shown in plain view inFIGS. 16A-16D, or combinations or extension of them, may be employed.

FIG. 16A shows a similar cylindrical structure 1600 as that of shown inFIG. 15 in a simplified schematic cross-sectional plan view of the powerchip without a cover. The cylindrical structure 1600 with a circularcross-section area includes of a substrate 1610, a PEM wall 1605, whichis positioned between catalyst layers 1615, 1620 serving as a cathodeand anode, respectively, in one embodiment. Formed in the center of thecylindrical structure 1600 is a flow path 1625 for flowing fuel oroxidant.

FIG. 16B shows the same components as that of FIG. 16A but in anon-circular cross-sectional plan view of a structure 1650, whichpermits more reactive surface area (i.e. wall length multiplied byheight) per unit of footprint area than does the cylindrical structurewith a circular cross-sectional area similar to the one shown in FIG.16A. However, the non-cylindrical shape may be at the expense of lessvolume available for flow of fuel or oxidant around the cathode if ahigh density array of non-cylindrical fuel cells is constructed.

FIG. 16C is an example of a curvilinear construction 1660 including thesame components as that of the cylindrical and rectangular counterparts.The curvilinear construction 1660 offers an even higher ratio ofreactive surface area per unit footprint area than the rectangular andcylindrical constructions. Furthermore, the curvilinear construction1660 can have one or more flow paths 1665 facilitating flow of fuel oroxidant as shown in FIG. 16C.

FIG. 16D is an example of fuel cell construction 1670 having aserpentine shape in plan view.

FIG. 17 is another cross-sectional diagram that indicates a furtherextension which is possible by etching fins 1710 onto the castellatedsurface. This embodiment shows a section of a PEM wall 1705 from above,which could be applied to any part of any of the general shapes shown inFIGS. 16A-16D. The fins 1710 can achieve a dramatic further increase insurface area. If the aspect ratio of the fins is too high, however, thefins may be less effective because of the increasing effectiveresistance of the proton conduction path. Furthermore, there may be alimit on the gains achievable from this method depending on thecharacteristics of the etching process employed. Note that the hydrogenmay be either dead-ended or flowing; oxygen flows in as well as out forwater removal via, for example, a manifold that is connected to a fuelcell having the PEM 1710 with the fins 1705.

FIGS. 18A through 18C are plan view diagrams showing how the reactivesurface area of the device, which is used in achieving high powerdensity, is further increased. The reactive surface area is increasedusing the constructions described above and can be further increased, asdescribed immediately below. FIG. 18A shows a standard planar PEM 1805typical of prior art planar fuel cells, which, for example, might havedimensions of 40 um by 400 um, with 16,000 μm² foot-print and reactivesurface area of 8000 μm². In FIG. 18B, creating a rectangular,three-dimensional PEM 1810 structure in accordance with an embodiment ofthe present invention on this same footprint yields 76,000 um², or morethan 4 times that of the planar PEM of the FIG. 18A. FIG. 18C shows howa castellation of the PEM wall 1815 can again double the surface area,producing 8 times the surface area of a planar design because thereactive surface area increases to 144,000 um². Since the cost of asemiconductor device tends to increase in proportion to the silicon“footprint” area employed, this high multiple results in correspondinglyhigher effective power density and lower cost per watt generated.

FIGS. 19A and 19B are diagrams that show a useful variation of the fuelcell design. As described above in reference to FIG. 1, an embodiment ofthe present invention is an array of fuel cells electricallyinterconnected and provided with gases and oxidants to separate flowpaths to form a power chip. The fuel cells interconnected to form thepower chip can include an array of any embodiment of fuel cellsdisclosed herein. The power chip may further include at least one plenumin gaseous communication with flow paths for distributing fuel oroxidant and one pair of terminals electrically coupled to the anodecatalyst of at least a subset of the array of power cells.

FIG. 19A is a diagram that depicts a power chip 1900 a including anarray of fuel cells 1905 a with a plurality of membranes 1922encompassing to three-dimensional geometric volumes (i.e., cylindrical),in the interior of the fuel cells 1905 a. Each PEM wall 1922 is coupledto a cover 1910 a, sealing the PEM wall 1922 and rendering each fuelcell 1905 dead-ended. Fuel is then flown into the three-dimensionalgeometric volumes of PEM wall 1922 to be in gaseous communication withanode catalyst 1915 a. Because cathode catalyst 1925 a is exposed toopen air 1920, the cathode catalyst 1925 a effectively has access tooxidant (e.g., oxygen) in the open air 1920 for reacting the fuel andoxidant at the power chip 1900 a to generate energy. The fuel cells ofthe power chip 1900 a can be divided into subsets, each subsetcontrolled by enabling and disabling electron flow to or from thesubset.

FIG. 19B is a diagram of power chip 1900 b that illustrates analternative cover configuration to the cover configuration in FIG. 19A.Here, the cover 1910 b is the “negative” of the cover 1910 a in FIG.19A. Instead of having a plurality of covers as shown in FIG. 19 a, thepower chip 1900 b may use one contiguous cover to be coupled to themembranes of the fuels cells. In such configuration, a flow path throughthe interior of the cylinders 1905 b is not dead-ended so that the powercell 1905 b can more effectively remove reaction by-products. In thisembodiment, the cathode 1925 b and anode 1915 b may be interchanged sothat water or other byproduct formed at the cathode may be removed morereadily.

A variation of the aforementioned designs may be useful in high-powersystems. In contrast to the configuration of FIG. 13, the substrate orwafer (also referred to herein as a power disk) is not designed to bedivided and packaged in small units. In one embodiment, the power diskcan include (1) an array of any embodiment of fuel cells disclosedherein, (2) at least one plenum in gaseous communication with flow pathsof the fuel cells to distribute the fuel and oxidant, (3) at least onepair of terminals electrically coupled to the anode and cathode catalystof at least a subset of the power cells to provide an interface toenergy generated by the power cells, and (4) at least one bus powerelectrically coupled to the terminals. The metal layer interconnectionsand control electronics (not shown) may be configured to connect toindividual fuel cells or substrate-wide. In one embodiment, the powerdisk can further include switches to interconnect the power chips in anelectrically selective manner. In a preferred embodiment, the power diskcan also include electronics to control the switches. It should be notedthat when the array of power cells is coupled to a substrate, the plenumis configured to distribute the fuel or oxidant with substantiallyuniform pressure. The plenum may be provided with at least one outlet sothat, for example, a byproduct of the reaction between the fuel, oxidantand the power cells can be removed. A plurality of these power disks maythen be stacked in an electrically parallel connection, forming a powerstack.

In one embodiment of the power chip, instead of electrical interconnectby wires or circuitry, the fuel cells are electrically connected by acoat or film of metal on both sides of the membranes. The coat of metalis in electrical communication with a terminal at one edge of the powerchip, where the terminal is connected to an external load.

In another embodiment of a power stack, the power stack can include asubstrate on which at least one power chip is coupled. The power chipcan be any embodiment of power chip disclosed herein. Yet anotherembodiment of a power chip can include a substrate, an array of anyembodiment of power cells disclosed herein, a pair of electrodes coupledto respective cathode and anode catalyst, and a pair of power disk buseselectrically coupled to the respective first electrode and therespective second electrode.

In one embodiment of a power stack, the power stack can include a powerstack a structure, a plurality of power disks connected to thestructure, and power stack terminals associated with the power stackstructure and configured to be electrically coupled to the diskterminals.

In one embodiment of the power stack, individual power disks 2005 a,2005 b may be stacked such a way that the flows of oxidant and fuelfacilitated by separate manifold as shown in FIG. 20A. For example,power disks 2005 a, 2005 b are fitted into a power stack structure 2045provided with a system of manifolds to provide paths for distributingfuel and oxidant to reach power disks. Power disks 2005 a, 2005 b arepositioned between upper plenums 2010 a, 2010 b and lower plenums 2015a, 2015 b. FIG. 20A shows that each power disk 2005 a, 2005 b includesone single individual power cell 2029 a, 2029 b for illustrativepurposes. Therefore, it should be understood that while not shown inFIG. 20A, each power disk 2005 a, 2005 b can include an array of powercells with other components for making a functional power disk.

Continuing to refer to FIG. 20A, the power stack is provided with afirst input chase 2025 for an entry point for fuel or oxidant. The firstinput chase 2025 has openings 2027 a, 2027 b so that the fuel or oxidantcan flow into upper plenums 2010 a, 2010 b. For example, once the flowof oxidant reaches the upper plenums 2010 a, 2010 b, the oxidant is incontact with the cathode catalyst 2031 a, 2031 b of the power cells 2029a, 2029 b, which is coupled to substrates 2041 a, 2041 b. Concurrently,a flow of fuel is entered via a second input chase 2030, which is openedto the lower plenums 2015 a, 2015 b. Here, the fuel makes contact withan anode catalyst 2033 a, 2033 b, triggering a reaction between thefuel, oxidant and catalyst for generating electrons. Each power disk2005 a, 2005 b can include electrodes electrically coupled to thecatalyst for electron transfer. Alternatively, the anode and cathodecatalyst can be assembled in the opposite configuration where thecomponents 2031 a, 2031 b are the anode catalyst, and the components2033 a, 2033 b are the cathode catalyst. In such a configuration, fuelis introduced via the first input chase 2025, and oxidant is introducedvia the second input chase 2030.

Furthermore, the flow path starting at the first input chase 2025disclosed in FIG. 20A is provided with an exit path. For example, oncethe spent fuel or oxidant passes through a flow path 2047 a, 2047 bafter reacting with respective catalyst, the fuel or oxidant flows to anexit plenum 2043 a, 2043 b. Passing through the exit plenums 2043 a,2043 b, the spent fuel or oxidant reaches an output chase 2040, which isprovided with an exit 2045. In one embodiment, this exit passage via theexit plenums 2043 a, 2043 b and via the output chase 2040 provides anoutlet for removing byproduct that is produced by the reaction betweenthe fuel, oxidant and the fuel cells.

Continuing to refer to FIG. 20A, the fuel or oxidant flow can besubstantially parallel to each power disk, and relatively littlepressure drop may be encountered. Because the individual reaction sitesare extremely small, the stochiometric amounts of reactant required ateach site are very small. Dead-ended, diffusion-based flow can be usedvery satisfactorily in many situations.

In FIG. 20B is a diagram of another embodiment of a power stack. Aplurality of power disks 2055 are coupled to a power stack structure1560, which, in this embodiment, is formed of two or more hollow paths.The power stack structure 2060, which may include stiffener (not shown)connected to both hollow posts of the example structure, is configuredto provide a fuel (e.g. hydrogen) flow path(s) 2070 (shown as dashedlines). The flow path(s) 2070 are in gaseous communication with a powerdisk entrance 2051 through which the fuel can flow into each power disks2055 via at least one disk manifold 2065. Because the power disks 2055are exposed to ambient air, the power disks 2055 have access to oxidant(i.e. oxygen) in the air. As such, without a deliberate supply ofoxidant through an oxidant flow in the power stack structure 2060 andmanifold in the power disks 2055, the power stack can sufficientlygenerate energy.

Power disks which are assembled according to such an arrangement cangenerate substantial power. FIGS. 21 and 22 illustrate examples.

FIG. 21 includes a sequence of fuel cell structures and associateddimensions that show how 10 KW per liter of volume can be obtained basedon a small amount of power density per reactive surface area.

FIG. 22 includes other diagrams with dimensions and weight that show asimilar calculation for watts/kg.

Controlling an Array of Power Generators

Power cells, such as fuel cells, generally possess a source impedance,and, hence, the voltage the devices can deliver is a function of currentbeing supplied. As a result, as a load demands more current, the loadtends to decrease the supply voltage that can be created by placing anumber of fuel cell devices in series. For example, with fuel cellshaving an open circuit potential of 0.9 volts and a maximum currentoutput capability of 1 milliampere (mA) at 0.4 volts, a seriesconnection of 12 such devices provides 4.8 volts at a maximum poweroutput of 4.8 mW, and a series connection of 6 such devices supplies 5.4volts at zero mW output. A power supply capacity of 1 ampere can becreated by connecting 1,000 series-connected columns of such imA devicestogether in parallel, assuming no internal losses.

Most electronic components require voltage regulation to within sometolerance, e.g., 5 volts±10%. In some prior art systems, voltageregulation is accomplished by external voltage regulators or othersimilar power conditioning circuits.

In some embodiments, an arrangement of power cells automaticallyswitches the number of series devices, obviating need for external powerregulators and, thereby, increasing energy efficiency, reducinggenerated heat, reducing circuit board space requirements, and reducingtotal cost of a system.

It is characteristic of fuel cells and many other power generators thattheir power conversion efficiency is higher at low power levels becausethere is less power dissipation inside the device. Depending on a shapeof a voltage-current (V-I) curve describing a power cell or equivalentcharacteristic, there may be a power level offering optimum efficiency.Typically for fuel cells, the optimum efficiency is as little voltagedrop as possible, hence minimum current. In this case, a trade-offexists between fuel efficiency and the number of power devices, hence,system cost and size.

Thus, an example optimal control technique for fuel cells according tosome embodiments of the present invention may include a coarse controlloop, which causes the number of series devices in each column to beadjusted so that the voltage is within tolerance for the actual load,and a fine control loop, which adds or subtracts the number of columnsof such devices that are connected in parallel to adjust the voltagefurther by moving the system up or down the V-I curve to supply thedesired current.

Further, in embodiments employing a feedback control system, a controltechnique may take into account individual, arrays, or banks of cells,which, when switched into or out of the power generating circuit,possess a transient response over time. Thus, a filter or other controllaw may be used in feedback loop(s) to ensure stable operation of thefeedback control system in the presence of load transients.

Further, the characteristics of the fuel cell devices, and,consequently, coefficients within a feedback filter or other controllaw, may depend upon the state of the fuel cell devices at precedingtimes or, ambient conditions of temperature, humidity, and pressure.

Example methods disclosed herein can be extended (i) to control current(i.e., constant current source rather than constant voltage source)delivery of multiple voltages or currents to support loads, such ascellular telephones, PDAs, and laptop computers, which typically requiremultiple voltages, and (ii) to track a time-varying set-point voltagerather than a constant set-point voltage. The tracking feature can beused, for example, to produce a 60 Hz sinusoidal power output directlyand efficiently or used as an audio amplifier to drive a speaker in acellular telephone directly and efficiently.

In some applications, it is useful to allocate power generated amongavailable fuel cell devices in a manner making efficient use of fuelwhile simultaneously delivering a required power profile to the load. Inportable power applications, such as laptop computers, PDAs, andcellular telephones, power requirements involve multiple voltages, eachcorresponding current varying with time, and often involving significanttransients in power requirement and a very large peak/average ratio. Asimilar requirement characterizes larger applications, such as powersources for automobiles and buses.

Commercial success of fuel cell power systems is expected to bedetermined by energy storage density (watt-hours/kilogram and watt-hoursper liter), peak and average power density (watts/liter andwatts/kilogram), and cost ($/watt, $/watt-hour). These metrics may beapplied to the complete system, including fuel storage, fuel delivery,and the fuel cells themselves.

Accordingly, an embodiment of the present invention includes a method orcorresponding apparatus to control operation of an assembly of manysmall fuel cells, each generating a small fraction of total powergenerated by the entire assembly, in such a manner that fuel consumptionover time is minimized, power output to a load is maintained withrequired regulation of voltage and/or current at one or multiplevoltages, and load transients are supported within required tolerance.In some embodiments, a control system employing the method orcorresponding apparatus takes into account variation of fuel cellperformance with temperature, humidity, and available gas pressures ofboth fuel and oxidant (e.g., due to variation with altitude), andadjusts control strategies, accordingly.

Another embodiment provides a method or corresponding apparatus tocontrol, such as optimally control, aggregate operation of an assemblyof many small power generators, where those generators may be fuelcells, micro-batteries, photo-electric, piezo-electric, other ambientvibration-driven devices, or any other source of power whose efficiencydepends upon a level of operation according to some characteristic thatis generally analogous to a battery discharge curve or a fuel cell V-Icurve. The control of the aggregate operation may be performed byoptimal control principles or other form of control principles.

Again, although the specifics of the following disclosure refer to fuelcells, the concepts, apparatus, or methods described should beinterpreted as applying to any such small or relatively small powergenerating device.

FIG. 23 shows a conventional, prior-art power supply circuit 2300 usinga fuel cell stack or battery as a prime power source 2301. A regulator2302 is employed to maintain a target voltage 2303 at a load 2304, wherethe target voltage is a voltage level within a range required for properoperation of the load 2304, such as 5 Vdc±0.5v. The regulator(s) areemployed because typically the voltage of the prime power source 2301varies with load in such a way that the target voltage cannot otherwisebe maintained. The regulator may be a three-terminal linear regulator,or any of several topologies of switching regulator (boost, buck,buck-boost) as commonly known in the art. A filter capacitor 2305 istypically employed to buffer transients caused by the load 2304 andabsorb power supply noise generated by the transients.

FIG. 24 is an illustration of a voltage-current (V-I) curve 2400 typicalof a micro-fuel cell. The curve 2400 expresses a variation of outputvoltage with current, or, implicitly, variation of output voltage withload impedance, in accordance with Ohm's Law. As is well known in theart, a fuel cell typically has three regions of operation: activationenergy dominated 2406, internal resistance dominated 2407, and masstransport dominated 2408. The entire curve 2400 tends to shift withtemperature, as indicated by a dashed line curve 2409 and with gaspressure and humidity. The voltage value at I=0 current is referred toas an Open Circuit Potential 2410.

Parallel Switching

With the V-I curve characteristics in mind, consider a circuit topology2500 shown in FIG. 25 which includes an array 2505 of fuel cells 2512,each having operational characteristics with a curve similar to thecurve 2400 illustrated in FIG. 24.

Referring to FIG. 25, the array 2505 contains a number ofseries-connected columns 2511 a, 2511 b, . . . , 2511×of fuel cells2512. Each column 251 a-x has a respective switch (2513 a, 2513 b, . . .2513×) between the fuel cells 2512 and a power bus 2515, such that whenthe switches 2513 a-x are closed, the corresponding series columns 2511a-x are connected in parallel with each other and a load 2514.

Consider first a situation where the leftmost switch 2513 a for theleftmost column 2511 a is closed and the others 2513 b-x are open. Ifthe impedance of the load 2514 is very high, then a voltage V₁ across aload is close to the sum of the open circuit potentials of theindividual cells comprising the series array. If the impedance of theload 2514 is lower, the current output by the fuel cells 2512 in theleftmost column 2511 a in this example, which substantially isequivalent to a load current, I₁, increases, and the voltage generatedby the column 2511 a of fuel cells 2512 decreases in accordance with thesum of the individual device V-I curves. Next, consider a situationwhere a second series column 2511 b is connected by closure of itscorresponding switch 2513 b. In this situation, the current flowingthrough each column 2511 a, 2511 b is reduced by roughly half, and thevoltage of each column 2511 a, 2511 b increases, correspondingly.Accordingly, an output voltage can be maintained within apre-established tolerance by connecting and disconnecting columns 2511a-x of cells 2512, which leads to a steady-state variation of voltage asa function of load impedance, as shown in FIG. 26.

FIG. 26 is a plot illustrating a situation in which a load impedance2614 is reduced and a load current 2615 correspondingly increases. As anincreasing number of columns 2616 are switched into the circuit (e.g.,array 2505 of FIG. 25), the circuit produces a saw-tooth variation involtage 2617 as a function of current 2615.

Series Switching

In many circumstances, a useful operating range of devices is muchgreater than the voltage tolerance. In this case, it may be useful toswitch the number of devices in each series column as well as the numberof columns.

FIG. 27 is a circuit topology 2700 that includes switches 2720 in acolumn topology 2718 that provides for selecting a varying number ofseries components 2719. This column topology may be repeated multipletimes in a parallel column topology to drive a load 2714 with finelyselectable levels of current.

Transient Response

Another consideration in the design of a control process is transientresponse of the individual devices. When initially switched into a loadcircuit, a device typically does not turn on fully instantly, butexperiences a transient response over time.

FIG. 28 is a plot illustrating a step function of an individual powergenerating device, such as a fuel cell. Connection of the powergenerating device to the load circuit at time T1 results in a rise incurrent flow that is exponential over time, illustrated by a solid linecurve 2821, with a time constant that is a function of the device. Theremay be an initial transport lag 2822 as well, depending on the state ofthe device, and, in the case of a fuel cell, distribution of ions in aProton Exchange Membrane (PEM). The initial transport lag may also be afunction of temperature and inactivity (i.e., how long ago the devicewas previously active). A typical variation with these latter parametersis shown as dashed curves 2823.

Transient responses for a fuel cell are influenced by an ability of thefuel cell to reach equilibrium. Areas in which equilibrium isestablished include: i) hydration of a membrane (e.g., Nafion) in areaction layer, ii) water balance in the reaction layer (e.g., is thereresidual liquid water in the pore space preventing gas from reachingcatalyst?), iii) oxidant/fuel supply (e.g., is there enough reactantgasses to support the desired load?), where areas ii and iii can berelated. Optimizing the operating conditions and architecture of theProton Exchange Membrane (PEM) is a factor in minimizing the transientresponse of a fuel cell.

The transient response may be either positive or negative. If themembrane is conditioned correctly and the cell has been inactive for aperiod of time, so that water in the pore space of the reaction layerhas been removed and the reacting gasses have had time to diffusethroughout the reaction layer and occupy all possible active catalystsites that otherwise would be isolated by trapped liquid water, thetransient response shows a peak power decrease with time. The decreasein power may be due to a build-up of liquid water in the pore space ofthe reaction layer that isolates active catalyst. Steady state powerresults when the accumulation of liquid water does not exceed itsremoval rate, but some level of water has accumulated in regions whereit is not easily removed. If the system has been dehydrated or there isdisruption in a reactant gas supply, then the transient shows a lessthan peak power and increases until steady state is reached. Once thesystem is at “steady state,” power fluctuates depending on operatingconditions and nature of construction. Thus, an ability to manage waterformation and its effect on reactant gas distribution throughout thereaction layer is useful for successfully operating fuel cells.

Consequently, it is useful that a control process take account of theseeffects and incorporate control filtering or a control law that does notresult in instability.

FIG. 29 is an electrical model of a fuel cell illustrated as anequivalent circuit 2900 in a general form. In addition to a transportlag 2924, there is typically an ohmic source resistance 2925, a secondresistance 2927 associated with activation losses, and a capacitance2926 resulting from the charge double layer at the electrodes.

Voltage Servo-Loop Structure

In some embodiments, a feedback filter or control law in the form ofcircuit elements or software, for example, may be used to compensatemeasured current by an inverse of a transfer function of the fuel cellor aggregate transfer function of multiple series or parallel fuel cellsin order to optimize or otherwise operate a control loop.Characteristics of the fuel cell or other power cell device may beestablished through characterization of the device across temperature,humidity, pressure, and load, and incorporated into Digital SignalProcessing using established methods of control theory and digitalsignal processing (DSP). Non-DSP devices and techniques may also beemployed. Sensors may be employed in the system to provide measures of,for example, temperature and humidity values, and these values may beused to index arrays of coefficients for the DSP filter or other controllaw. The coefficients may be tuned adaptively, such as by means of aneural network, in which improved operation of the fuel cell under eachset of ambient conditions alters linkage of neural network nodes (i.e.,series-column and multiple parallel columns of fuel cells).

FIG. 30 is a block diagram of an example control structure to control anarray of fuel cells 3038 or other forms of power cells. There may be aset-point voltage 3029 which the array 3038 delivers to a load 3030 oftime-varying impedance. The voltage delivered to the load by the array3038 may be sensed 3031 and fed back to switching logic 3032 through anappropriate filter 3033 or state space equations. This filter mayoperate with an input state vector 3033, including voltages sensed atvarious points 3037 in the array of fuel cells 3038. The input statevector 3020 may include states in the form of analog or digitalrepresentations from temperature sensor(s) 3015 and relative humiditysensors 3016 a, 3016 b. The DSP filter block 3033 may operate on thestate vector 3020 by applying a matrix operation following customarypractice, where a matrix (not shown) applied to the state vector 3020during the matrix operation may represent an appropriately modifiedinverse of a discrete transfer function, H(z), describing the fuel cellarray 3038 and, in some embodiments, may also account for a model of theload 3030, as understood in feedback control systems arts.

A resulting filtered output (“command”) voltage 3035 from the DSP filterblock 3033 and the set point voltage 3029 are together presented to theswitching control block 3032, which may be conveniently implemented as amemory array in which addresses may be a function of the filtered outputand set-point voltages, and data 3026 in the memory 3025 may be binarywords used to control which switches 3036 in the array 3038 are on(i.e., closed) and which are off (i.e., open). In one embodiment, forexample, each combination of command and set-point voltage values 3035,3029 is mapped to exactly one location in the memory 3025, and thatlocation contains a bit pattern (not shown) of which switches 3036 areon and which are off. The contents of the memory array may be refreshedor modified under control of a supervisory processor 3027 running asupervisory control process that controls temperature, output humidity,and other factors as noted below. The contents of the memory array mayalso be received from an external system (not shown).

The comparator switch control block 3032 may execute a switching processusing a specific sequence of instructions executed in a computer,combinatorial logic, parallel implementation of combinatorial logicimplemented in logic gates, and so forth, which may be implemented inthe form of both a coarse loop, which switches the number of seriescomponents as a function of both load voltage 3031 and load current3034, and a fine loop, which switches the number of parallel columns3005 a, 3005 b active in the array 3038. The fine loop may add columns3005 a, 3005 b when the filtered load voltage 3035 drops below athreshold and may remove columns 3005 a, 3005 b when the filtered loadvoltage 3035 rises above a threshold. If the system departs by more thansome tolerance from an optimal or other point on the V-I curve from anenergy-efficiency point of view, for example, or if it approaches astate where most of the parallel columns 3005 a, 3005 b are in use, thenan additional row of series elements 3007 can be switched into thecircuit in accordance with the coarse loop. Similarly, if the system istoo lightly loaded, then a row can be removed by the coarse or fineloops.

Route Around Failed Cells

Occasionally, an individual fuel cell degrades or fails. In aseries-connected column 3005 a, 3005 b, the total column voltage is thesum of the individual voltages of the cells at whatever current ispassing through them. Since the current is the same in each, it is thecurrent corresponding to the lowest-performing cell in the column. Thissituation can be detected by means of small, current-sensing resistors3010 a, 3010 b in each column 3005 a, 3005 b of FIG. 30 to producerespective voltages 3032′, or, alternatively, by sensing voltage 3037 atmultiple points in the columns 3005 a, 3005 b and checking foruniformity. If significant non-uniformity is detected, then it is likelythat one or more cells 3007 are dissipating excess energy, and theswitch control block 3032 can remove them from use by “delisting” anentire row from its memory 3025, for example, as long as other columnsavailable can meet the electrical current demand. Other techniques, suchas requiring use of fewer series-column cells but using more columns, ifavailable, may also be possible, depending on which cell in the seriescolumn is faulty.

Many applications of interest may include a battery or a capacitor tohandle peak loads that exceed the capacity of the fuel cell array whichmust meet average load, or to meet transient requirements that exceedthe response time of the cells. If the peak/average ratio of the loadprofile is small, then a capacitor 3038 can support transients, as shownin FIG. 26. If the peak/average ratio is high (as for example with ahard disk, or a sensor which communicates by radio every so often), thena rechargeable battery can support the peak periods in which the activesurface area of the array is not sufficient to provide the peak currentload. In this case, care may be taken to manage the charge/dischargecycle or the battery properly. Most battery types can support a limitednumber of charge/discharge cycles. The battery may thus dischargethrough a number of cycles before being recharged. In order to maximizebattery life, this number should be as large as possible, given theexcess fuel cell capacity available to recharge (i.e., peak energy andpeak frequency vs. fuel cell capacity excess over non-peak load). Thecontrol process may monitor battery voltage and determine the rechargepoint based upon either predetermined parameters or recent historicalbehavior of the load.

FIG. 31 is a flow chart showing features of an example control processusing example coarse and fine control loops. After a timer interrupt ofa “fast” timer, which causes repeating the control process 3100 at arelatively fast rate, the process 3100 starts (3105). It should beunderstood that other forms of interrupts, such as on-demand and/or anevent driven interrupt, may also cause the process 3100 to start. In acoarse portion 3101 of the process 3100, determinations are made withregard to large changes in current (or voltage) with which to drive aload. This entails removing rows from an array (3115) or adding rows tothe array (3125) based on whether the load voltage is sensed asexceeding a high limit (3110) or being less than a low limit (3120). Ina fine portion (3102) of the process 3100, determinations (3130, 3140)are made as to whether to remove (3135) or add (3145) parallel columnsfrom or to the array, respectively, to remove or add current by fineamounts. The process 3100 ends (3150) thereafter.

Temperature/Humidity Servo-Loop Structure

Further servo-loop considerations arise from a variation of the V-Icurve with temperature, pressure, and humidity. For example, in manyapplications, it is preferable that air output from a Hydrogen-air fuelcell be at a humidity and temperature that does not result incondensation of vapor into water. Accordingly, a control process mayfirst check output humidity, and, if it is too high, raise the operatingtemperature set-point which, for the same water output, lowers RelativeHumidity (RH). Lowering the relative humidity can be accomplished bygenerating the same power from fewer fuel cells, which can beeffectuated, for example, by altering the data 3026 in a look-up table(not shown) in the memory 3025 of the control block 3032 of FIG. 30. Aseparate loop may then compare the operating temperature to itsset-point and make adjustments to the table, accordingly. However, fuelefficiency may best be served by keeping the operating temperature aslow as possible by minimizing internal resistive losses. The temperatureset-point is thus driven by the control process to be as low as possibleunless this creates a humidity problem.

With some fuel cell structures, there may be an optimum concentration ofpower (i.e., quantity of active cells), driven by increased dissipationwith increasing power versus less dissipation with higher temperature.

Basing a control loop on concentration of power can be used both toincrease temperature during start-up and to maintain optimal temperatureduring operation. If the system is operating below its current sourcingcapacity, then the control system optionally cycles through the variousavailable columns, so the columns remain at a reasonable, uniform,average temperature.

FIG. 32 is a flow diagram of an example process to change operatingparameters of an array of fuel cells based on temperature orconsiderations presented immediately above. FIG. 32 is a flow diagram ofa process 3200 that occurs at a slower rate that the process 3100 ofFIG. 31. Referring to FIG. 32, a timer interrupt (slow) or other form ofinterrupt (3205) starts the process 3200. A determination is made as towhether an output humidity is greater than a high limit (3210). If theoutput humidity is less than the high limit (3210), the process 3200compares the output humidity to a low limit (3215). If the outputhumidity is greater than the high limit (3210), the process 3200increases a set point temperature (3220) to reduce the output humidity.If the output humidity is less than the low limit (3215), the process3200 attempts to decrease the set point temperature (3225).

The process 3200 may also be configured to monitor the temperature at aset point plus, optionally, hysteresis of a temperature (3230). If thetemperature is less than the set point (plus hysteresis), the process3200 determines whether the temperature is less than the set point(minus hysteresis) 3235. If the temperature is greater than the setpoint (plus hysteresis) (3230), a new switching table to cool the powercells may be loaded (3240). If the temperature is less than the setpoint (minus hysteresis) (3235), the process 3200 may load a newswitching table to cause the power cells to warm (3245) by driving theload. As previously described (i.e., less or more catalyst surfacearea), to warm or cool the power cells typically means that fewer ormore power cells are used to drive a load.

The process 3200 may also include rotating banks of power cells orcolumns of power cells to drive a load. A determination of whether tocycle to different units in the array may be made (3250) through use ofan internal clock or counter (not shown). If it is time (3250), theprocess 3200 may load (3255) a new switching table in a processor orstorage area that is accessed to determine which power cells to use fordriving the load. If it is not time to cycle to a different unit in thearray (3250), the process 3200 increments a cycle counter (3260).Thereafter, the process 3200 tests or reads a voltage, V_(sense) forfailed power cells. If the power cells are determined to be functioningproperly such as by monitoring an output current or voltage (3265), theprocess 3200 exits (3275). If the power cells are determined to befaulty (3265), the process 3200 calculates a new switching table andloads it (3270). The process 3200 exits (3275) after that.

It should be understood that the flow diagrams of FIGS. 31 and 32 aremerely examples. The number of decisions, order, flow, or other aspectsof the flow diagrams may be modified, changed, or otherwise set forthwithout departing from the scope of the example embodiments of FIGS. 31and 32. Moreover, it should be understood that the flow diagrams may beimplemented in hardware, firmware, or software. If implemented insoftware, the software may be written in any form of software andexecuted by any processor suitable to work in the context of the powergeneration as disclosed herein. It should also be understood that thesoftware can be implemented in the form of instructions stored on anyform of computer readable medium, such as RAM, ROM, magnetic or opticalmedium, and so forth loaded by a processor, and executed to cause theprocessor to perform the processes 3100, 3200 or variations thereof asunderstood in the art.

Rotation of Cells to Improve Life

A further set of decisions to consider in operating an array of fuelcells or other power generating cells may be made based on a time ortime-integral of power (energy) basis to rotate active cells among alarger quantity available in an array of fuel or power cells. Rotationof active cells logic is typically executed at a less frequent rate thanthe voltage control loop of FIG. 31.

Power Optimization

As described in reference to FIGS. 30 and 31, a coarse voltage controlloop, which changes the number of cells or banks of cells in series, canbe operated in combination with a fine voltage control loop whichchanges the number of columns of cells or banks of cells in parallel, tocontrol aggregate output power by an array of power cells. A reason forthis choice of control of the array may be the following. A typicalvoltage range per device may be from 0.9 volts open circuit potential toabout 0.4 volts at maximum output, and typical current may be 1 milliampor less, depending on Reactive Surface Area (RSA) in the case of fuelcells. In this situation, series switching of power cells in a columnmay be best used as a coarse adjustment, and parallel switching ofcolumns may be best used as a fine adjustment. Implementation of coarseand fine control loops is described immediately below in reference toFIGS. 33 and 34.

FIG. 33 is a plot of multiple V-I curves that vary with the number offuel cells in series combination (i.e., a column). Current through eachcell in the series is the same, and the voltage adds. The V-I curve maythus be translated upward, and its slope increases because of additionalsource impedance introduced by each series element. Curves 3339, 3340,and 3341, in that order, represent an increase in a number of seriescells. A line 3342 represents load voltage versus current according toOhm's law, V=IR_(L), for a particular value of load resistance R_(L).The intersections of this line 3342 with the V-I curves are therespective operating points for that load resistance. So, addition offuel cell(s) in series, while the load remains constant, changes thevoltage and current from, for example, the intersection of load line3342 with V-I curve 3339 to the intersection of the load line 3342 withcurve 3340.

FIG. 34 illustrates an effect of stacking the cells in parallel. Curves3442, 3443, and 3444 represent increasing a number of cells in parallel.In this case, the load voltage 3442 is the same, and the currentincreases through the reduced source impedance.

Since the number of series devices is typically small (e.g., four to sixfor a 3.3 volt supply), whereas the quantity in parallel is large (e.g.,1000 for a 1 ampere supply), the change in voltage resulting from addinga column is typically far less than the change in voltage from adding arow, allowing tighter regulation.

Beyond simple voltage regulation, the system may make optimal use ofenergy stored in the fuel by operating the system efficiently.

FIGS. 35A and 35B are plots that illustrate an example relationshipbetween operating point, delivered power, and dissipated power. FIG. 35Ais essentially a repeat of the V-I curve shown in FIG. 24. FIG. 35Bshows total power 3545 generated from fuel oxidation, total powerexclusive of activation losses 3545′, power delivered to the load 3546,and power dissipated in the device 3547. The activation energy isassumed to be constant with current I; hence, the dissipated anddelivered power are governed by V_(INT) 3548, the point at which anextension of the approximately linear, resistive region of the V-I curveintercepts the V-axis.

Total power 3545 to a first approximation,P _(TOT) =V _(INT) I+P _(ACT)

Excluding activation losses P_(ACT), which are small and roughlyconstant with current I, P_(TOT) is a linear function of I with a slopeof 1, as shown in the FIGS. 35A and 35B.

Power delivered to the load isP _(del) =V(I)IP _(del)=(V _(INT) −R _(S) I)I=IV _(INT) −I ² R _(S)

where R_(S)=the source resistance of the device.

Power dissipated in the device is:P _(diss) =P _(TOT) −P _(del) =V _(INT) I−(IV _(INT) −I ² R _(S))P _(diss) =I ² R _(S)

For devices having a V-I curve as shown in FIG. 35A, the delivered poweris quadratic in current and downward-concave, producing a maximumdelivered power at a point 3549, where P_(del)=P_(diss).

Optimum Power: Minimize Current per Cell

Dissipated power is quadratic in current and upward-concave, indicatingthat the lower the current, the less dissipation that occurs. But, lowercurrent means proportionally more devices are required. Optimumefficiency is the ratio of delivered power to total power. Efficiencythus decreases monotonically with current.

As a practical matter, operating stability and other design factors mayresult in choice of a slightly higher current operating point, dependingon the detailed characteristics of a particular device, which are notpart of the simple model above. In a practical system, optimumefficiency may also be limited because the less current per device, themore devices and, therefore, the more cost associated with the system.

Optimum Power: Switch Smallest Possible Increments

FIGS. 36A and 36B are a circuit diagram 3648 and current waveform 3649,respectively, that illustrate another lesson that may be drawn from thequadratic nature of the dissipated and delivered power. In a situationwhere a device is switched on and off at a 50% duty cycle to deliveraverage power VI by alternating between zero current and 2I current forequal time intervals, the power dissipated during the on times is fourtimes as much for half the time, or twice as much on average. First,consider a constant current output 3650, which delivers power I²R_(L),and dissipates power I²R_(S). Now, consider curve 3652, in which thesource current to a filter capacitor is switched between 0 and 2I with afifty percent duty cycle. The average current delivered to the load 3651is still I, and varies only slightly at the filter capacitor output3653. However the dissipated power is:P _(dis)=(2I)² R _(s)/2=2I ² R _(S),which is twice as much as the constant current output (3650).

In other words, in order to minimize power consumption, the controlprocess switches as few devices as possible to maintain the set-pointvoltage. The example control process disclosed above does that.

Further, it follows that the smaller the individual devices, or thegroups of devices which are independently switched, the more efficientthe system is in its conversion of energy.

Multiple Voltage Outputs

FIG. 37 is a topology of a multi-voltage supply 3700 formed from a power(e.g., fuel) cell array 3705 configured as multiple subarrays or banks3710 a, 3710 b, . . . , 3710 n. The multi-voltage supply 3700 is anextension of the disclosed structure, which useful in electronic deviceswhich require multiple voltages. A modern cell phone or laptop computer,for example, contains multiple voltage regulators to provide differentvoltages to the display, logic hard disk, RF devices, etc. An array ofmicro fuel cells or other power generating cells can easily beconfigured to deliver such multiple voltages without incurring the powerdissipation, heat generation, board cost and separate component costassociated with a conventional power conditioning system in a phone orlaptop. It should be understood that the fuel cell array 3705 may beconfigured with extra banks (e.g., 3710 n−2, 3710 n−1, and 3710 n) toprovide redundancy, where the extra banks may be configurable to provideany of the voltages provided by primary banks. Moreover, all of thebanks 3710 a-n may be configurable to supply any voltages to allow forrotation of the banks for longevity purposes.

Current Source, AC Power Source, Audio Power Amplifier

Several further extensions of the basic structure are also possible: thesystem may be configured to maintain constant current with varyingvoltage (i.e., a current source instead of a voltage source, which isuseful for powering certain types of sensors, for example); the systemmay track not a constant voltage or current but instead track a timevarying set-point, thus providing an AC power source, for example, at 60Hz for back-up power to a household; or, the system may track an audiofrequency signal to form a very efficient power amplifier, for example,to drive a speaker in a cellular phone. This arrangement may be the sameas the arrangement in FIG. 30 except that the constant set-point voltage3029 is replaced with a time-varying input.

Fabrication in the Power Chip

Using the MEMs structures and fabrication methods on a silicon substratewhich are described in prior Marsh patents (U.S. Pat. Nos. 6,312,846 and6,815,110), it may be cost effective to incorporate the control systemdescribed above on the same silicon substrate as the fuel cells, withminimal increase in silicon surface area. First, a series of layers maybe deposited, patterned, and etched upon the substrate, followingestablished conventional semiconductor fabrication practice, which mayproduce transistor switches for the power array, voltage and currentsensors, and an array of gates implementing the control process.Alternatively, a structure comprising an FPGA or embedded processorCentral Processing Unit (CPU) plus memory may be employed. A FieldProgrammable Gate Array (FPGA) configuration or program memory may beRead Only Memory (ROM), One time Programmable (OTP) memory, or FLASHmemory, as desired, depending upon the need to customize the device fordifferent applications after manufacture. Using current CMOS fabricationmethods, any of these approaches may use a silicon area, which is smallcompared to a 1 cm² fuel cell array, and can easily be built on the samesilicon area under the MEMs fuel cell structures.

Hierarchical Control of Power Disks, Power Stacks

For larger power sources, Marsh (U.S. Pat. Nos. 6,312,846 and 6,815,110)notes that a plurality of power cells may be assembled on a power disk,and a plurality of power disks may be assembled into a power stack. Inthis situation, a hierarchical control system may be implemented, inwhich each power chip is controlled in accordance with an exampleembodiment of the invention, but with set-points determined by a similarcontrol system that operate at the power disk level upon the individualpower chips. Similarly, a plurality of power disks may be controlled tooptimize their aggregate power output when they are assembled into apower stack.

Power Amplifier

FIG. 38 is a block diagram of a system 3800 using power generators toperform a function of an amplifier that would normally use voltagerails. In this example, an external device 3805 produces a low levelvoltage signal 3835 received by the amplifier 3810. The amplifier 3810includes a high impedance input stage 3815, power generation cellscontroller 3820, electronics power cells 3825, and signal generationpower cells 3830. The modules 3815, 3820, 3825, 3830 are interconnectedin any typical manner understood in the art such as through integrationon a single silicon wafer and interconnected as previously describedabove. The high impedance input stage 3815 and power generation cellscontroller 3820 are powered by the electronics power cells 3825 whichprovides sufficient power to operate the electronics in the amplifier3810. The high impedance input stage 3815 provides a representation 3817of the input waveform 3835 to the power generation cells controller3820, which, in turn, controls the signal generation power cells 3830 ina manner to produce a voltage or current waveform 3840 as an amplifiedform of the input waveform 3835. The output waveform 3830 may be used todrive a load 3845, which may be a headset speaker in a cell phone, forexample, or other form of load having electrical characteristicssuitable to be driven by the example amplifier 3810.

FIG. 39 is a diagram of a pair of waveforms 3900 that illustrate anexample use of the power generation cells that are controlled to producea waveform. The pair of waveforms 3900 includes a sinusoidal powerwaveform 3905 and an adjusted power waveform 3910. The adjusted powerwaveform 3910 is produced in a shape that compensates for effects of aload 3915 waveform 3905. It should be understood that the adjustedwaveform 3910 is merely an arbitrary example of an adjusted waveformthat is not necessarily to scale or expected to be implemented inpractice. It is should also be understood that the adjusted waveform3910 may be used for purposes of improving a power factor or powerquality as understood in the power delivery arts.

FIG. 40 is a block diagram of an array 4000 of power cells (not shown)having A-I columns of power cells 4010 a, 4010 b, 4010 c, . . . 4010 i.The array 4000 also includes a controller 4005 either on a substrateintegrated with the power cells or separate from the substrate with thepower cells. In either case, the controller may be used to control whichcolumn(s) 4010 a-i are used to deliver power 4020 via a bus 4015 to aload 4025. In other words, the controller 4005 may sequence through thecolumns 4010 a-i or otherwise select columns of power cells to generatepower 4020 to deliver to the load 4025. In the example embodiment, thecontroller 4005 sequentially steps from columns A-I to generate powerand accordingly, the power 4020 is delivered in a corresponding order(i.e., column A 4010 a has power Pa delivered first, column B 4010 bnext delivers power P_(b), . . . , and finally column 14010 i deliverspower Pi).

FIG. 41 is a block diagram that illustrates a case in which a powergeneration system 4110 includes a controller 4105 associated with anarray of power cells 4107, 4110 a-e. In this example, starter cells 4107are caused first to generate power Pout 4120 via a bus 4115 to anexternal load 4125 to cause the starter cells 4107 to generate heat soas to warm surrounding, and outwardly extending, power cells 4110 a.Alternatively, the starter cells 4107 may be caused to deliver powerPwarm 4122 to an optional internal load 4140 on the same substrate 4102as the array of power cells. This allows the starter cells 4107 to warmup without having to be connected to an external load 4125. It should beunderstood that the location of the starter cells 4107 may be set inother locations among power cells in the array 4110 a-e, such as morecentric to warm power cells in any of four directions.

In operation, the controller 4105 may receive temperature feedback 4135from the starter cells. As the temperature increases, as determined bythe controller 4105 as a function of the temperature feedback 4135, thecontroller 4105 may engage power generation cells 4110 a surrounding thestarter cells 4107. Then, as the surrounding cells 4110 a warm, thecontroller 4105 may engage a next set of power cells 4110 b surroundingthe starter cells 4110 a to engage and produce power 4120 to deliver tothe external load 4125 via the bus 4115. This process may continue untilall of the power generation cells 4110 a-e are activated to generatepower 4120 to deliver to the external load 4125.

It should be understood that the progression, as represented by an arrow4130, may not be diagonal as illustrated but, instead, each of the zones4107 and 4110 a-e may be vertical sectors of power cells as illustratedin FIG. 40 or FIG. 30. In whichever embodiment is selected, it should beunderstood that the starter cells 4107 may be driven with a lowefficiency to generate heat efficiently to have a rapid warm up time,and each of the subsequent subsets of power cells that are activated mayalso be driven with a given efficiency to have a rapid or normal rate ofwarming to match a given profile for starting the power cells for use ina given environment.

FIG. 42 is a block diagram of a controller 4200 with two levels offunctions, kernel functions 4205 and “higher” functions 4210. The kernelfunctions 4205 may be basic power management and control functions thatare used, for example, to map voltage levels to corresponding switchclosures and also convert power requests into a number of rows incolumn(s) and/or parallel columns to produce the power by selectingwhich switches to close to configure series and parallel combinations ofpower cells. Other basic functions may also be employed within thekernel functions 4205.

The higher functions 4210 may include functions that provide intelligentcontrol of the power cells. Examples of higher functions include coldstart, sinewave control, arbitrary waveform control, voltage regulation,current regulation, rotation of power cells, adjustment, anddecontamination. Vibration, as discussed below in reference to FIG. 43may also be an example of a higher function as assist with acceleratingcorrection of a “flooding” event.

In one example embodiment, the controller 4200 has the higher functions4210 provide requests 4225 to the kernel functions 4205 to perform oneof the aforementioned functions or other high level functions. In turn,the kernel functions 4205 present control signals 4215 to switches orother control elements, such as fuel or oxidant flow control elements(e.g. MEMs switches), to execute the requests 4225. Feedback 4220 may bereturned to the kernel functions 4205, which, in turn, present thefeedback 4230 in a form suitable for reading by the higher functions4210. Alternatively, the feedback 4220 may be presented directly to thehigher functions 4210.

It should be understood that the controller 4200 may be segmented inother ways and include other functions suitable for use with a singlepower cell or array of power cells.

The controller 4200 may also include inter-controller or intra-orinter-power disk/chip communication module(s) 4212 to allow multiplecontrollers to act in a unified or distributed manner. Inter-disk/chipcommunications may also provide support for redundancy or vast arrays ofvirtually unlimited numbers of power cells.

FIG. 43 is a schematic diagram of a system 4300 that includes a powercell 4305, electrically coupled to a pulse generator 4310, formed withpower cells or, optionally, an electronic pulse generator, through apair of switches 4315 a, 4315 b. The switches 4315 a, 4315 b areutilized in this embodiment to switch the power cell 4305 fromdelivering power to a load 4312 to receiving a pulse 4325 a or pulses4325 a, 4325 b from the pulse generator 4310. It should be understoodthat the pulse generator 4310 may be any form of signal generator toproduce a typical or atypical waveform, such as a sinewave, chirp, orother waveform.

The purpose of the pulse 4325 a is to apply a voltage or current tocatalyst on the sides of the walls. By driving the catalyst with thepulses 4325 a, 4325 b, contaminant that may have settled on the catalystmay be ejected, as represented by multiple arrows 4330 projectingoutward from the power cell. It should be understood that a similar setof a multiple arrows 4330 may also be occurring inside the volumeencompassed by the power cell 4305, but not shown for ease ofunderstanding how the decontamination process works. Further, it shouldbe understood that either pulse 4325 a, 4325 b may also be a referencelevel, such as a ground potential, to decontaminate one catalyst sidemore than the other.

Additionally, a 1 volt or other low voltage waveform may be used tocause a catalyst coated membrane, which may be a very thin film, used toform the power cell 4305 to vibrate. Vibration may be used to acceleratea removal of a flood condition that can impair power generation by thepower cell 4305. To that end, the power cell 4305 may be speciallydesigned in thickness, height, diameter, catalyst thickness, segmented,or other physical parameter, to increase its ability to vibrate.Moreover, vibration (or heat) may be used to increase energy for use incausing, accelerating or otherwise affecting a reaction taking place inat the power cell 4305, and the power cell 4305 may be driven atamplitude(s) or offsets at single-or multi-frequencies to improve energydelivery or reduction for a particular reaction or step in a reaction.

In terms of testing, the power cell 4305 has an electrical impedance,similar to a capacitor, since it has two “plates” (outside and insidewalls of the membrane) in the form of electrically conductive catalyst.The impedance can be used for automated testing, where a controller canbe employed to switch electrical paths from the power cell 4305 to pinsat an edge of a power chip or disk connected to a capacitance meter. Inthis way, a vast array of power cells can be quickly tested ordiagnosed.

Further, a control program implemented in a custom gate array or ASIChierarchical structure in which a plurality of power cells arecontrolled as in an array of microprocessor generators described aboveand assembled to create a power disk, where similar processes controlallocation of power generation to power cells on the disk. In someembodiments, the hierarchical structure in which a plurality of powerdisks are controlled and assembled to create a power stack, wheresimilar processes control the allocation of power generation to powerdisks in the stack.

It should be understood that any of the aforementioned control filters,control laws, or alternative control laws, such as optimal control,fuzzy logic, neural networks, H-infinity control, and so forth, can beexecuted in the form of software in a processor to control the operationof power generation. Hardware or firmware implementations may also beemployed. The control program may, in addition to the control describedabove, optionally be adaptive to power cell characteristics over time asindividual or banks of devices age over time. The control program mayalso be modified or upgraded after field installation or manufacturingto give previously identical devices different operating characteristicsintended for different applications.

In one embodiment, the array of micro-power generators may be configuredas a hybrid system including a rechargeable battery, capacitor,photovoltaic, vibration-harvesting generator, etc. The battery chargingcycle may be configured to enhance long battery life.

Electro-Chemical Application of Power Cells

One embodiment of another aspect of the invention is a method ofreacting reaction components. One example method includeselectro-chemically reacting reaction components on opposite sides of atleast one membrane encompassing a respective volume in a presence of atleast one catalyst. The method referred to here can be facilitated anyembodiment of power cells, power chip, power disk or power stackdisclosed herein.

FIG. 44 illustrates an example of this embodiment of the method in theinvention. A power cell 4400 includes the same or similar components asthe ones described above in reference to other power cells, includinganode catalyst 4405, cathode catalyst 4410, and a membrane 4415 (e.g.,an ion or proton exchange membrane). The power cell 4400 can be coupledto a substrate 4420, through which a reaction component can flow asindicated by an arrow 4440. The membrane 4415 referred herein can belaminate of a non-woven fabric and a membrane, such as an ion exchangemembrane or an proton exchange membrane. Similar to the power cellsconfigured to form a three-dimensional geometric structure, the membraneencompasses a volume 4425. In micro-power cell applications, the volume4425 may be less than one cubic millimeter. In other applications, thevolume 4425 may be less than one cubic centimeter, one cubic meter, oreven less than one cubic micrometer. An electrical circuit that includesa switch 4455 and a load 4457 may be connected to the cathode 4410 andanode 4405. In conjunction with another reaction component 4445 in or onthe opposite side of the separator 4415, the power cell 4400 can inducean electrochemical reaction. For example, the power cell 4400 can beused for performing use of electrolysis of water to produce a hydrogen:2H₂O_((l))→2H_(2(g))+O_(2(g))

Electrolysis of water can be conducted by passing current generated bythe power cell 4400 through drop(s) of water 4440 (in practice asaltwater solution increases the reaction intensity making it easier toobserve). Hydrogen gas is seen at the cathode 4410 using platinumelectrodes, and oxygen bubbles at the anode 4405, also using platinumelectrodes. If other metals are used as the anode, there is a chancethat the oxygen will react with the anode instead of being released as agas. For example using iron electrodes in a sodium chloride solutionelectrolyte, iron oxide is produced at the anode, which reacts to formiron hydroxide. Other industrial uses include electrometallurgy, theprocess of reduction of metals from metallic compounds to obtain thepure form of metal using electrolysis. For example, sodium hydroxide inits metallic form is separated by electrolysis into sodium and hydrogen,both of which have important chemical uses. Also this example method canbe applied to manufacture aluminium, lithium, sodium, potassium, oraspirin. Another practical use of electrolysis by a power cell isanodization. It makes the surface of metals resistant to corrosion. Forexample, ships in water are saved from being corroded by oxygen in waterby this process, which is done with the help of electrolysis. Thisprocess is also used to make surfaces more decorative.

Furthermore, the hydrogen gas that is generated by the electrolysis ofwater can be used to fuel other additional reaction. For example, thehydrogen gas 4460 can be flown through an exit 4470 and collected as afuel.

While the use of electrolysis described above is provided in a contextof a power cell, such method can also be applied to an array of powercells, a power disk, or power disk, or power stack.

Another embodiment of the method further includes applying a potentialdifference for conducting an electro-chemical reaction. Continuing torefer to FIG. 44, by turning on a switch 4480, the power cell 4400 canbe electrically connected to a battery 4482. However, the battery 4480is for illustrative purposes. Therefore, other form of power can beapplied to the power cell 4400 such as DC, AC, fixed frequency,arbitrary waveform or any combination thereof.

Applying a potential difference to an anode and a cathode can induce aelectro-chemical reaction. For example, a power cell that includes amembrane made of material such as Nafion®, can vibrate when a current,such as a sinusoidal, pulse, chirp, or other waveform, is appliedtherethrough. As such, applying a potential difference through the powercell 4400 can induce or enhance an electro-chemical reaction such as forgenerating heat (i.e., at the membrane 4415), and converting a physicalstate (i.e., liquid, pseudo-solid, gas, pseudo-liquid, or solid) toanther physical state, and changing a profile of the potentialdifference during difference stages of a reaction or within a singlestage of a reaction. When the potential difference is applied to anarray of power cells, it is also possible to apply the potentialdifference to a subset of the array in thermal proximity to the subjectthat is generating heat.

It is also possible to employ a sensor to monitor the electro-chemicalreaction. For example, the system 4401 can include a sensor 4406 formeasuring the level of hydrogen gas inside of a housing 4403 during theelectrolysis of water. In turn, the system can be equipped with a feedback system by monitoring feedback of a metric associated with thereaction (e.g., concentration or temperature) or power cells (e.g.,temperature or pressure) to a typical reaction. Monitoring of theelectro-chemical reaction using the feedback system can be useful toadjust, regulate and/or control an electro-chemical reaction as afunction at least one metric. Metrics can include temperature, pressure,humidity, time, concentration of at least one of the reactioncomponents, for example. Further, one can regulate when and how to applythe potential difference. For example, an electro-chemical reaction candecelerate or accelerate by decreasing or increasing the potentialdifference, respectively, in typical reaction.

Furthermore, a product of an electro-chemical reaction can be outputtedusing such manner as extracting, expelling, draining, releasing orventing another electro-chemical reaction can follow during or after thefirst electro-chemical reaction. Introducing at least one other reactioncomponent during or after the first electro-chemical reaction cantrigger a new electro-chemical reaction or be used in a next stage ofthe ongoing electro-chemical reaction. And the product of the newelectro-chemical reaction can be also outputted in a similar manner asthe earlier electro-chemical reaction.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A power cell comprising: (a) a membrane, with a first side and asecond side, having a three-dimensional geometric structure encompassinga volume; (b) a cover coupled to the membrane to separate a first flowpath from a second flow path at the membrane; (c) first and secondcatalyst in gaseous communication with respective first flow path andsecond flow path and in ionic communication with respective first andsecond sides of the membrane; and (d) a first electrode electricallycoupled to the first catalyst on the first side of the membrane and asecond electrode electrically coupled to the second catalyst on thesecond side of the membrane.
 2. The power cell of claim 1 furthercomprising a substrate to which the membrane is coupled.
 3. The powercell of claim 2 wherein at least a portion of at least one of the flowpaths is perpendicular to the substrate.
 4. The power cell of claim 1wherein at least a portion of the first flow path is perpendicular to atleast a portion of the second flow path.
 5. The power cell of claim 1wherein at least a portion of the first flow path is parallel to atleast a portion of the second flow path.
 6. The power cell of claim 1wherein at least one end of the volume is open-ended.
 7. The power cellof claim 1 wherein the membrane is a proton exchange membrane.
 8. Thepower cell of claim 1 wherein the geometric structure is a cylindricallyshaped structure in a plan view.
 9. The power cell of claim 1 whereinthe geometric structure is a non-cylindrically shaped structure in aplan view to increase reactive surface area for the catalyst on themembrane relative to a cylindrically shaped structure in a plan view.10. The power cell of claim 1 wherein the geometric structure has acurvilinear cross-sectional plan view.
 11. The power cell of claim 1wherein the geometric structure has a castellated cross-sectional planview segment.
 12. The power cell of claim 1 wherein the geometricstructure defines fins for at least a given length of the geometricstructure.
 13. The power cell of claim 1 wherein the geometric structurehas a serpentine cross sectional plan view segment.
 14. The power cellof claim 1 wherein the geometric structure has a rectangular crosssectional plan view.
 15. The power cell of claim 1 wherein the first andsecond catalyst is in at least a portion of the respective first andsecond sides of the membrane, the first and second catalyst electricallyisolated by at least a portion of the membrane.
 16. The power cell ofclaim 1 wherein the cover is made of a different material from that ofthe membrane.
 17. The power cell of claim 1 wherein the cover is madefrom a gas impermeable material.
 18. The power cell of claim 1 whereinthe cover is a membrane including first and second sides with catalystin ionic communication with the membrane and in electrical communicationwith the electrodes to make the cover an active cover.
 19. The powercell of claim 1 further comprising a circuit element in communicationwith the power cell via at least one of the electrodes to enable anddisable electron flow to or from the first or second catalyst.
 20. Thepower cell of claim 1 wherein fuel and oxidant are introduced to thefirst and second catalyst via the first flow path and second flow path,respectively.
 21. The power cell of claim 1 wherein oxidant and fuel areintroduced to the first and second catalyst via the first flow path andsecond flow path, respectively.
 22. The power cell of claim 1 whereinthe first and second catalyst include a same material.
 23. The powercell of claim 1 wherein the first and second catalyst include adifferent material.
 24. The power cell of claim 1 wherein the first orsecond flow path leads to an outlet path to remove byproduct from thefirst or second flow path produced by a reaction between fuel, oxidant,and the first and second catalyst.
 25. The power cell of claim 1 whereinthe power cell is an autonomous structure.
 26. A method of generatingenergy using a power cell comprising flowing fuel or oxidant through avolume encompassed by an ion exchange membrane of the power cell. 27.The method of claim 26 wherein flowing the fuel or oxidant includesflowing the fuel through the volume.
 28. The method of claim 26 whereinflowing the fuel or oxidant includes flowing the oxidant through thevolume.
 29. The method of claim 26 further comprising flowing the fuelor oxidant through a substrate to which the power cell is coupled. 30.The method of claim 26 further comprising controlling operation of thepower cell by enabling and disabling electron flow to or from the powercell.
 31. The method of claim 26 wherein the volume of the first flowpath at the power cell has a cross-sectional plan view selected from agroup consisting of: circular, non-circular, curvilinear, serpentine,rectangular, and optionally castellated or including fins for at least agiven length of the power cell.
 32. The method of claim 26 furtherincluding reacting the fuel and oxidant with substantially an entiretyof the power cell.
 33. The method of claim 26 wherein flowing the fuelor oxidant through the volume has a substantially negligibledifferential pressure from an input of the volume to an output of thevolume.
 34. The method of claim 26 wherein the pressure differential isless than 1 psi.
 35. A power cell comprising: a) means for encompassinga volume; b) means for separately flowing fuel and oxidant inside thevolume and outside of the volume; c) means for maintaining separation ofthe fuel and oxidant at the volume; d) means for reacting the fuel andoxidant to provide free electrons; and e) means for carrying theelectrons to a load. 36-93. (canceled)